{"id":32426,"date":"2024-11-25T09:18:03","date_gmt":"2024-11-25T01:18:03","guid":{"rendered":"https:\/\/fwq.ai\/blog\/32426\/"},"modified":"2024-11-25T09:18:03","modified_gmt":"2024-11-25T01:18:03","slug":"%e7%90%86%e8%a7%a3javascript%e4%b8%ad%e7%9a%84%e4%bd%9c%e7%94%a8%e5%9f%9f","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/32426\/","title":{"rendered":"\u7406\u89e3JavaScript\u4e2d\u7684\u4f5c\u7528\u57df"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/000\/887\/227\/169348422780933.jpg\" class=\"aligncenter\" title=\"\u7406\u89e3JavaScript\u4e2d\u7684\u4f5c\u7528\u57df\u63d2\u56fe\" alt=\"\u7406\u89e3JavaScript\u4e2d\u7684\u4f5c\u7528\u57df\u63d2\u56fe\" \/><\/p>\n<p>\u8303\u56f4\uff0c\u6216\u786e\u5b9a\u53d8\u91cf\u6240\u5728\u4f4d\u7f6e\u7684\u4e00\u7ec4\u89c4\u5219\uff0c\u662f\u4efb\u4f55\u7f16\u7a0b\u8bed\u8a00\u7684\u6700\u57fa\u672c\u6982\u5ff5\u4e4b\u4e00\u3002\u4e8b\u5b9e\u4e0a\uff0c\u5b83\u662f\u5982\u6b64\u57fa\u672c\uff0c\u4ee5\u81f3\u4e8e\u6211\u4eec\u5f88\u5bb9\u6613\u5fd8\u8bb0\u8fd9\u4e9b\u89c4\u5219\u662f\u591a\u4e48\u5fae\u5999\uff01<\/p>\n<p>\u51c6\u786e\u7406\u89e3 JavaScript \u5f15\u64ce\u5982\u4f55\u201c\u601d\u8003\u201d\u4f5c\u7528\u57df\u5c06\u4f7f\u60a8\u907f\u514d\u7f16\u5199\u63d0\u5347\u53ef\u80fd\u5bfc\u81f4\u7684\u5e38\u89c1\u9519\u8bef\uff0c\u8ba9\u60a8\u505a\u597d\u51c6\u5907\u4e13\u6ce8\u4e8e\u95ed\u5305\uff0c\u5e76\u8ba9\u60a8\u79bb\u6c38\u8fdc\u4e0d\u518d\u7f16\u5199\u9519\u8bef\u66f4\u8fd1\u4e00\u6b65 \u518d\u6b21\u3002<\/p>\n<p>&#8230;\u65e0\u8bba\u5982\u4f55\uff0c\u5b83\u4f1a\u5e2e\u52a9\u60a8\u7406\u89e3\u63d0\u5347\u548c\u5173\u95ed\u3002 <\/p>\n<p>\u5728\u672c\u6587\u4e2d\uff0c\u6211\u4eec\u5c06\u4e86\u89e3\uff1a<\/p>\n<p><span>\u7acb\u5373\u5b66\u4e60<\/span>\u201c\u201d\uff1b<\/p>\n<ul>\n<li>JavaScript \u4e2d\u4f5c\u7528\u57df\u7684\u57fa\u7840\u77e5\u8bc6<\/li>\n<li>\u89e3\u91ca\u5668\u5982\u4f55\u51b3\u5b9a\u54ea\u4e9b\u53d8\u91cf\u5c5e\u4e8e\u54ea\u4e2a\u4f5c\u7528\u57df<\/li>\n<li>\u540a\u88c5\u7684\u5b9e\u9645\u5de5\u4f5c\u539f\u7406<\/li>\n<p> <em><\/em> <\/p>\n<li>ES6 \u5173\u952e\u5b57 let \u548c const \u5982\u4f55\u6539\u53d8\u6e38\u620f\u89c4\u5219<\/li>\n<\/ul>\n<p>\u8ba9\u6211\u4eec\u6df1\u5165\u63a2\u8ba8\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6709\u5174\u8da3\u4e86\u89e3\u6709\u5173 ES6 \u7684\u66f4\u591a\u4fe1\u606f\u4ee5\u53ca\u5982\u4f55\u5229\u7528\u8bed\u6cd5\u548c\u529f\u80fd\u6765\u6539\u8fdb\u548c\u7b80\u5316 JavaScript \u4ee3\u7801\uff0c\u4e3a\u4ec0\u4e48\u4e0d\u770b\u770b\u8fd9\u4e24\u95e8\u8bfe\u7a0b\uff1a<\/p>\n<h2>\u8bcd\u6cd5\u8303\u56f4<\/h2>\n<p>\u5982\u679c\u60a8\u4e4b\u524d\u7f16\u5199\u8fc7\u4e00\u884c JavaScript\uff0c\u60a8\u5c31\u4f1a\u77e5\u9053<em><\/em>\u5b9a\u4e49\u53d8\u91cf\u7684\u4f4d\u7f6e\u51b3\u5b9a\u4e86\u60a8\u53ef\u4ee5<em>\u4f7f\u7528<\/em>\u7684\u4f4d\u7f6e&gt; \u4ed6\u4eec\u3002\u53d8\u91cf\u7684\u53ef\u89c1\u6027\u53d6\u51b3\u4e8e\u6e90\u4ee3\u7801\u7684\u7ed3\u6784\uff0c\u8fd9\u4e00\u4e8b\u5b9e\u79f0\u4e3a<em>\u8bcd\u6cd5<\/em> <em>\u8303\u56f4\u3002<\/em><\/p>\n<p>\u5728 JavaScript \u4e2d\u521b\u5efa\u4f5c\u7528\u57df\u6709\u4e09\u79cd\u65b9\u6cd5\uff1a<\/p>\n<ol>\n<li> <strong>\u521b\u5efa\u51fd\u6570<\/strong><strong><\/strong>\u3002\u5728\u51fd\u6570\u5185\u90e8\u58f0\u660e\u7684\u53d8\u91cf\u4ec5\u5728\u8be5\u51fd\u6570\u5185\u90e8\u53ef\u89c1\uff0c\u5305\u62ec\u5728\u5d4c\u5957\u51fd\u6570\u4e2d\u3002<\/li>\n<li> <b>\u4f7f\u7528 let \u6216 const <strong>\u5728\u4ee3\u7801\u5757\u5185<\/strong>\u58f0\u660e\u53d8\u91cf\u3002\u6b64\u7c7b\u58f0\u660e\u4ec5\u5728\u5757\u5185\u53ef\u89c1\u3002<strong><\/strong> <\/b> <\/li>\n<li> <strong>\u521b\u5efa<\/strong>catch <strong>\u5757<\/strong>\u3002\u4e0d\u7ba1\u4f60\u76f8\u4fe1\u4e0e\u5426\uff0c\u8fd9\u5b9e\u9645\u4e0a<em>\u786e\u5b9e<\/em>\u521b\u5efa\u4e86\u4e00\u4e2a\u65b0\u7684\u8303\u56f4\uff01<\/li>\n<\/ol>\n<pre>\"use strict\";\nvar mr_global = \"Mr Global\";\n\nfunction foo () {\n    var mrs_local = \"Mrs Local\";\n    console.log(\"I can see \" + mr_global + \" and \" + mrs_local + \".\");\n    \n    function bar () {\n        console.log(\"I can also see \" + mr_global + \" and \" + mrs_local + \".\");\n    }\n}\n\nfoo(); \/\/ Works as expected\n\ntry {\n    console.log(\"But \/I\/ can't see \" + mrs_local + \".\"); \n} catch (err) {\n    console.log(\"You just got a \" + err + \".\");\n}\n\n{\n    let foo = \"foo\";\n    const bar = \"bar\";\n    console.log(\"I can use \" + foo + bar + \" in its block...\");\n}\n\ntry {\n    console.log(\"But not outside of it.\");   \n} catch (err) {\n    console.log(\"You just got another \" + err + \".\");\n}\n\n\/\/ Throws ReferenceError!\nconsole.log(\"Note that \" + err + \" doesn't exist outside of 'catch'!\") \n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u4e0a\u9762\u7684\u4ee3\u7801\u7247\u6bb5\u6f14\u793a\u4e86\u6240\u6709\u4e09\u79cd\u4f5c\u7528\u57df\u673a\u5236\u3002\u60a8\u53ef\u4ee5\u5728 Node \u6216 Firefox \u4e2d\u8fd0\u884c\u5b83\uff0c\u4f46 Chrome \u8fd8\u65e0\u6cd5\u4e0e let \u5f88\u597d\u5730\u914d\u5408\u3002<\/p>\n<p>\u6211\u4eec\u5c06\u8be6\u7ec6\u8ba8\u8bba\u5176\u4e2d\u7684\u6bcf\u4e00\u4e2a\u3002\u8ba9\u6211\u4eec\u9996\u5148\u8be6\u7ec6\u4e86\u89e3 JavaScript \u5982\u4f55\u786e\u5b9a\u54ea\u4e9b\u53d8\u91cf\u5c5e\u4e8e\u54ea\u4e2a\u4f5c\u7528\u57df\u3002<\/p>\n<h2>\u7f16\u8bd1\u8fc7\u7a0b\uff1a\u9e1f\u77b0<\/h2>\n<p>\u5f53\u60a8\u8fd0\u884c\u4e00\u6bb5 JavaScript \u65f6\uff0c\u4f1a\u53d1\u751f\u4e24\u4ef6\u4e8b\u4f7f\u5176\u6b63\u5e38\u5de5\u4f5c\u3002<\/p>\n<ol>\n<li>\u9996\u5148\uff0c\u7f16\u8bd1\u60a8\u7684\u6e90\u4ee3\u7801\u3002<\/li>\n<li>\u7136\u540e\uff0c\u7f16\u8bd1\u540e\u7684\u4ee3\u7801\u5c06\u88ab\u6267\u884c\u3002<\/li>\n<\/ol>\n<p>\u5728<em>\u7f16\u8bd1<\/em><em>\u6b65\u9aa4<\/em>\u671f\u95f4\uff0cJavaScript \u5f15\u64ce\uff1a<\/p>\n<ol>\n<li>\u8bb0\u4e0b\u6240\u6709\u53d8\u91cf\u540d\u79f0<\/li>\n<li>\u5c06\u5b83\u4eec\u6ce8\u518c\u5230\u9002\u5f53\u7684\u8303\u56f4<\/li>\n<li>\u4e3a\u81ea\u5df1\u7684\u4ef7\u503c\u89c2\u4fdd\u7559\u7a7a\u95f4<\/li>\n<\/ol>\n<p>\u53ea\u6709\u5728<em>\u6267\u884c<\/em>\u671f\u95f4\uff0cJavaScript \u5f15\u64ce\u624d\u771f\u6b63\u5c06\u53d8\u91cf\u5f15\u7528\u7684\u503c\u8bbe\u7f6e\u4e3a\u7b49\u4e8e\u5176\u8d4b\u503c\u3002\u5728\u90a3\u4e4b\u524d\uff0c\u5b83\u4eec\u662f undefined\u3002 <\/p>\n<h3>\u7b2c 1 \u6b65\uff1a\u7f16\u8bd1<\/h3>\n<pre>\/\/ I can use first_name anywhere in this program \nvar first_name = \"Peleke\";\n\nfunction popup (first_name) {\n    \/\/ I can only use last_name inside of this function\n    var last_name = \"Sengstacke\";\n    alert(first_name + ' ' + last_name);\n}\n\npopup(first_name);\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u8ba9\u6211\u4eec\u9010\u6b65\u4e86\u89e3\u4e00\u4e0b\u7f16\u8bd1\u5668\u7684\u4f5c\u7528\u3002<\/p>\n<p>\u9996\u5148\uff0c\u5b83\u8bfb\u53d6\u884c var first_name = &#8220;Peleke&#8221;\u3002\u63a5\u4e0b\u6765\uff0c\u5b83\u786e\u5b9a\u5c06\u53d8\u91cf\u4fdd\u5b58\u5230\u7684<em>\u8303\u56f4<\/em>\u3002\u56e0\u4e3a\u6211\u4eec\u4f4d\u4e8e\u811a\u672c\u7684\u9876\u5c42\uff0c\u6240\u4ee5\u5b83\u610f\u8bc6\u5230\u6211\u4eec\u5904\u4e8e<em>\u5168\u5c40\u8303\u56f4<\/em>\u3002\u7136\u540e\uff0c\u5b83\u5c06\u53d8\u91cf first_name \u4fdd\u5b58\u5230\u5168\u5c40\u8303\u56f4\uff0c\u5e76\u5c06\u5176\u503c\u521d\u59cb\u5316\u4e3a undefined\u3002<\/p>\n<p>\u5176\u6b21\uff0c\u7f16\u8bd1\u5668\u8bfb\u53d6\u5e26\u6709 function popup (first_name) \u7684\u884c\u3002\u56e0\u4e3a <em>function<\/em> \u5173\u952e\u5b57\u662f\u8be5\u884c\u7684\u7b2c\u4e00\u4e2a\u5185\u5bb9\uff0c\u56e0\u6b64\u5b83\u4e3a\u51fd\u6570\u521b\u5efa\u4e00\u4e2a\u65b0\u4f5c\u7528\u57df\uff0c\u5c06\u51fd\u6570\u7684\u5b9a\u4e49\u6ce8\u518c\u5230\u5168\u5c40\u4f5c\u7528\u57df\uff0c\u5e76\u67e5\u770b\u5185\u90e8\u4ee5\u67e5\u627e\u53d8\u91cf\u58f0\u660e\u3002<\/p>\n<p>\u679c\u7136\uff0c\u7f16\u8bd1\u5668\u627e\u5230\u4e86\u4e00\u4e2a\u3002\u7531\u4e8e\u6211\u4eec\u51fd\u6570\u7684\u7b2c\u4e00\u884c\u4e2d\u6709 var last_name = &#8220;Sengstacke&#8221;\uff0c\u56e0\u6b64\u7f16\u8bd1\u5668\u4f1a\u5c06\u53d8\u91cf last_name \u4fdd\u5b58\u5230 class=&#8221;inline&#8221;&gt;popup \u2014<em>\u4e0d<\/em>\u5230\u5168\u5c40\u8303\u56f4 \u2014 \u5e76\u5c06\u5176\u503c\u8bbe\u7f6e\u4e3a undefined\u3002 <\/p>\n<p>\u7531\u4e8e\u51fd\u6570\u5185\u4e0d\u518d\u6709\u53d8\u91cf\u58f0\u660e\uff0c\u7f16\u8bd1\u5668\u5c06\u9000\u56de\u5230\u5168\u5c40\u4f5c\u7528\u57df\u3002\u7531\u4e8e\u4e0d\u518d\u6709\u53d8\u91cf\u58f0\u660e\uff0c\u56e0\u6b64\u6b64\u9636\u6bb5\u5df2\u5b8c\u6210\u3002<\/p>\n<p>\u8bf7\u6ce8\u610f\uff0c\u6211\u4eec\u5b9e\u9645\u4e0a\u8fd8\u6ca1\u6709\u8fd0\u884c\u4efb\u4f55\u4e1c\u897f\u3002<em><\/em>\u6b64\u65f6\u7f16\u8bd1\u5668\u7684\u5de5\u4f5c\u53ea\u662f\u786e\u4fdd\u5b83\u77e5\u9053\u6bcf\u4e2a\u4eba\u7684\u540d\u5b57\uff1b\u5b83\u4e0d\u5173\u5fc3\u4ed6\u4eec\u505a\u4ec0\u4e48\u3002 <\/p>\n<p>\u6b64\u65f6\uff0c\u6211\u4eec\u7684\u7a0b\u5e8f\u77e5\u9053\uff1a<\/p>\n<ol>\n<li>\u5168\u5c40\u8303\u56f4\u5185\u6709\u4e00\u4e2a\u540d\u4e3a first_name \u7684\u53d8\u91cf\u3002<\/li>\n<li>\u5168\u5c40\u8303\u56f4\u5185\u6709\u4e00\u4e2a\u540d\u4e3a popup \u7684\u51fd\u6570\u3002<\/li>\n<li>\u5728 popup \u8303\u56f4\u5185\u6709\u4e00\u4e2a\u540d\u4e3a last_name \u7684\u53d8\u91cf\u3002<\/li>\n<li>first_name \u548c last_name \u7684\u503c\u5747\u4e3a undefined\u3002<\/li>\n<\/ol>\n<p>\u5b83\u5e76\u4e0d\u5173\u5fc3\u6211\u4eec\u662f\u5426\u5728\u4ee3\u7801\u4e2d\u7684\u5176\u4ed6\u5730\u65b9\u5206\u914d\u4e86\u8fd9\u4e9b\u53d8\u91cf\u503c\u3002\u5f15\u64ce\u5728\u6267\u884c\u65f6\u4f1a\u5904\u7406\u8fd9\u4e2a\u95ee\u9898\u3002<\/p>\n<h3>\u7b2c 2 \u6b65\uff1a\u6267\u884c<\/h3>\n<p>\u5728\u4e0b\u4e00\u6b65\u4e2d\uff0c\u5f15\u64ce\u518d\u6b21\u8bfb\u53d6\u6211\u4eec\u7684\u4ee3\u7801\uff0c\u4f46\u8fd9\u4e00\u6b21\uff0c<em>\u6267\u884c<\/em>\u5b83\u3002 <\/p>\n<p>\u9996\u5148\uff0c\u5b83\u8bfb\u53d6\u884c var first_name = &#8220;Peleke&#8221;\u3002\u4e3a\u6b64\uff0c\u5f15\u64ce\u4f1a\u67e5\u627e\u540d\u4e3a first_name \u7684\u53d8\u91cf\u3002\u7531\u4e8e\u7f16\u8bd1\u5668\u5df2\u7ecf\u7528\u8be5\u540d\u79f0\u6ce8\u518c\u4e86\u4e00\u4e2a\u53d8\u91cf\uff0c\u5f15\u64ce\u4f1a\u627e\u5230\u5b83\uff0c\u5e76\u5c06\u5176\u503c\u8bbe\u7f6e\u4e3a &#8220;Peleke&#8221;\u3002<\/p>\n<p>\u63a5\u4e0b\u6765\uff0c\u5b83\u8bfb\u53d6\u884c function popup (first_name)\u3002\u7531\u4e8e\u6211\u4eec\u6ca1\u6709\u5728\u8fd9\u91cc\u6267\u884c\u8be5\u51fd\u6570\uff0c\u56e0\u6b64\u5f15\u64ce\u4e0d\u611f\u5174\u8da3\u5e76\u8df3\u8fc7\u5b83\u3002<\/p>\n<p>\u6700\u540e\uff0c\u5b83\u8bfb\u53d6\u884c popup(first_name)\u3002\u7531\u4e8e\u6211\u4eec<em><\/em>\u5728\u8fd9\u91cc\u6267\u884c\u4e00\u4e2a\u51fd\u6570\uff0c\u56e0\u6b64\u5f15\u64ce\uff1a<\/p>\n<ol>\n<li>\u67e5\u627e popup \u7684\u503c <\/li>\n<li>\u67e5\u627e first_name \u7684\u503c <\/li>\n<li>\u5c06 popup \u4f5c\u4e3a\u51fd\u6570\u6267\u884c\uff0c\u5e76\u4f20\u9012 first_name \u7684\u503c\u4f5c\u4e3a\u53c2\u6570<\/li>\n<\/ol>\n<p>\u5f53\u6267\u884c popup \u65f6\uff0c\u5b83\u4f1a\u7ecf\u5386\u76f8\u540c\u7684\u8fc7\u7a0b\uff0c\u4f46\u8fd9\u6b21\u662f\u5728\u51fd\u6570 popup \u5185\u3002\u5b83\uff1a<\/p>\n<ol>\n<li>\u67e5\u627e\u540d\u4e3a last_name \u7684\u53d8\u91cf <\/li>\n<li>\u5c06 last_name \u7684\u503c\u8bbe\u7f6e\u4e3a\u7b49\u4e8e &#8220;Sengstacke&#8221; <\/li>\n<li>\u67e5\u627e alert\uff0c\u5c06\u5176\u4f5c\u4e3a\u51fd\u6570\u6267\u884c\uff0c\u5e76\u4ee5 &#8220;Peleke Sengstacke&#8221; \u4f5c\u4e3a\u53c2\u6570<\/li>\n<\/ol>\n<p>\u4e8b\u5b9e\u8bc1\u660e\uff0c\u5e55\u540e\u53d1\u751f\u7684\u4e8b\u60c5\u6bd4\u6211\u4eec\u60f3\u8c61\u7684\u8981\u591a\u5f97\u591a\uff01<\/p>\n<p>\u65e2\u7136\u60a8\u5df2\u7ecf\u4e86\u89e3\u4e86 JavaScript \u5982\u4f55\u8bfb\u53d6\u548c\u8fd0\u884c\u60a8\u7f16\u5199\u7684\u4ee3\u7801\uff0c\u6211\u4eec\u5c31\u51c6\u5907\u597d\u89e3\u51b3\u4e00\u4e9b\u66f4\u8d34\u8fd1\u5b9e\u9645\u7684\u95ee\u9898\uff1a\u63d0\u5347\u7684\u5de5\u4f5c\u539f\u7406\u3002<\/p>\n<h2>\u663e\u5fae\u955c\u4e0b\u7684\u540a\u88c5<\/h2>\n<p>\u8ba9\u6211\u4eec\u4ece\u4e00\u4e9b\u4ee3\u7801\u5f00\u59cb\u3002<\/p>\n<pre>bar();\n\nfunction bar () {\n    if (!foo) {\n        alert(foo + \"? This is strange...\");\n    }\n    var foo = \"bar\";\n}\n\nbroken(); \/\/ TypeError!\nvar broken = function () {\n    alert(\"This alert won't show up!\");\n}\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5982\u679c\u8fd0\u884c\u6b64\u4ee3\u7801\uff0c\u60a8\u4f1a\u6ce8\u610f\u5230\u4e09\u4ef6\u4e8b\uff1a<\/p>\n<ol>\n<li>\u5728\u5206\u914d\u4e4b\u524d\uff0c\u60a8<em>\u53ef\u4ee5<\/em>\u5f15\u7528 foo\uff0c\u4f46\u5176\u503c\u4e3a undefined\u3002<\/li>\n<li>\u60a8\u53ef\u4ee5\u5728\u5b9a\u4e49\u4e4b\u524d\u8c03\u7528 \u5df2\u635f\u574f\u7684\uff0c\u4f46\u60a8\u4f1a\u6536\u5230 TypeError\u3002<\/li>\n<li>\u60a8<em>\u53ef\u4ee5<\/em>\u5728\u5b9a\u4e49\u4e4b\u524d\u8c03\u7528 bar\uff0c\u5b83\u4f1a\u6309\u9700\u8981\u5de5\u4f5c\u3002<\/li>\n<\/ol>\n<p><strong>\u63d0\u5347<\/strong>\u662f\u6307 JavaScript \u4f7f\u6211\u4eec\u58f0\u660e\u7684\u6240\u6709\u53d8\u91cf\u540d\u79f0\u5728\u5176\u4f5c\u7528\u57df\u5185\u7684<em>\u4efb\u4f55\u5730\u65b9<\/em>\u90fd\u53ef\u7528\uff0c\u5305\u62ec\u5728\u6211\u4eec\u5206\u914d\u7ed9\u5b83\u4eec\u4e4b\u524d<em><\/em> .<\/p>\n<p>\u4ee3\u7801\u6bb5\u4e2d\u7684\u4e09\u79cd\u60c5\u51b5\u662f\u60a8\u5728\u81ea\u5df1\u7684\u4ee3\u7801\u4e2d\u9700\u8981\u6ce8\u610f\u7684\u4e09\u79cd\u60c5\u51b5\uff0c\u56e0\u6b64\u6211\u4eec\u5c06\u4e00\u4e00\u9010\u6b65\u4ecb\u7ecd\u5b83\u4eec\u3002<\/p>\n<h3>\u63d0\u5347\u53d8\u91cf\u58f0\u660e<\/h3>\n<p>\u8bf7\u8bb0\u4f4f\uff0c\u5f53 JavaScript \u7f16\u8bd1\u5668\u8bfb\u53d6\u50cf var foo = &#8220;bar&#8221; \u8fd9\u6837\u7684\u884c\u65f6\uff0c\u5b83\u4f1a\uff1a<\/p>\n<ol>\n<li>\u5c06\u540d\u79f0 foo \u6ce8\u518c\u5230\u6700\u8fd1\u7684\u8303\u56f4<\/li>\n<li>\u5c06 foo \u7684\u503c\u8bbe\u7f6e\u4e3a\u672a\u5b9a\u4e49<\/li>\n<\/ol>\n<p>\u6211\u4eec\u53ef\u4ee5\u5728\u8d4b\u503c\u4e4b\u524d\u4f7f\u7528 foo \u7684\u539f\u56e0\u662f\uff0c\u5f53\u5f15\u64ce\u67e5\u627e\u5177\u6709\u8be5\u540d\u79f0\u7684\u53d8\u91cf\u65f6\uff0c\u5b83<em>\u786e\u5b9e<\/em>\u5b58\u5728\u3002\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u5b83\u4e0d\u4f1a\u629b\u51fa ReferenceError\u3002 <\/p>\n<p>\u76f8\u53cd\uff0c\u5b83\u83b7\u53d6\u503c undefined\uff0c\u5e76\u5c1d\u8bd5\u4f7f\u7528\u8be5\u503c\u6267\u884c\u60a8\u8981\u6c42\u7684\u4efb\u4f55\u64cd\u4f5c\u3002\u901a\u5e38\uff0c\u8fd9\u662f\u4e00\u4e2a\u9519\u8bef\u3002<\/p>\n<p>\u8bb0\u4f4f\u8fd9\u4e00\u70b9\uff0c\u6211\u4eec\u53ef\u80fd\u4f1a\u60f3\u8c61 JavaScript \u5728\u6211\u4eec\u7684\u51fd\u6570 bar \u4e2d\u770b\u5230\u7684\u66f4\u50cf\u662f\u8fd9\u6837\uff1a<\/p>\n<pre>function bar () {\n    var foo; \/\/ undefined\n    if (!foo) {\n        \/\/ !undefined is true, so alert\n        alert(foo + \"? This is strange...\");\n    }\n    foo = \"bar\";\n}\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5982\u679c\u60a8\u613f\u610f\u7684\u8bdd\uff0c\u8fd9\u662f<strong>\u63d0\u5347\u7684\u7b2c\u4e00\u6761\u89c4\u5219<\/strong>\uff1a\u53d8\u91cf<em>\u5728\u5176\u6574\u4e2a\u8303\u56f4\u5185<\/em>\u90fd\u53ef\u7528\uff0c\u4f46\u5176\u503c\u4e3a undefined \uff0c\u76f4\u5230\u60a8\u4ee3\u7801\u5206\u914d\u7ed9\u4ed6\u4eec\u3002<\/p>\n<p>\u5e38\u89c1\u7684 JavaScript \u4e60\u60ef\u7528\u6cd5\u662f\u5c06\u6240\u6709 var \u58f0\u660e\u5199\u5165\u5176\u4f5c\u7528\u57df\u7684\u9876\u90e8\uff0c\u800c\u4e0d\u662f\u9996\u6b21\u4f7f\u7528\u5b83\u4eec\u7684\u4f4d\u7f6e\u3002\u7528 Doug Crockford \u7684\u8bdd\u6765\u8bf4\uff0c\u8fd9\u53ef\u4ee5\u5e2e\u52a9\u60a8\u7684\u4ee3\u7801<em>\u9605\u8bfb<\/em>\u66f4\u50cf\u5b83<em>\u8fd0\u884c<\/em>\u3002<\/p>\n<p>\u4ed4\u7ec6\u60f3\u60f3\uff0c\u8fd9\u662f\u6709\u9053\u7406\u7684\u3002\u5f53\u6211\u4eec\u4ee5 JavaScript \u8bfb\u53d6\u4ee3\u7801\u7684\u65b9\u5f0f\u7f16\u5199\u4ee3\u7801\u65f6\uff0c\u4e3a\u4ec0\u4e48 bar \u7684\u884c\u4e3a\u65b9\u5f0f\u975e\u5e38\u6e05\u695a\uff0c\u4e0d\u662f\u5417\uff1f\u90a3\u4e48\u4e3a\u4ec0\u4e48\u4e0d\u4e00\u76f4\u8fd9\u6837\u5199\u5462\uff1f <\/p>\n<h3>\u63d0\u5347\u51fd\u6570\u8868\u8fbe\u5f0f<\/h3>\n<p>\u4e8b\u5b9e\u4e0a\uff0c\u5f53\u6211\u4eec\u5728\u5b9a\u4e49\u4e4b\u524d\u5c1d\u8bd5\u6267\u884c broken \u65f6\uff0c\u6211\u4eec\u5f97\u5230\u4e86 TypeError\uff0c\u8fd9\u53ea\u662f\u7b2c\u4e00\u6761\u63d0\u5347\u89c4\u5219\u7684\u4e00\u4e2a\u7279\u4f8b\u3002<\/p>\n<p>\u6211\u4eec\u5b9a\u4e49\u4e86\u4e00\u4e2a\u540d\u4e3a broken \u7684\u53d8\u91cf\uff0c\u7f16\u8bd1\u5668\u4f1a\u5728\u5168\u5c40\u8303\u56f4\u5185\u6ce8\u518c\u8be5\u53d8\u91cf\uff0c\u5e76\u5c06\u5176\u8bbe\u7f6e\u4e3a\u7b49\u4e8e undefined\u3002\u5f53\u6211\u4eec\u5c1d\u8bd5\u8fd0\u884c\u5b83\u65f6\uff0c\u5f15\u64ce\u4f1a\u67e5\u627e broken \u7684\u503c\uff0c\u53d1\u73b0\u5b83\u662f undefined\uff0c\u5e76\u5c1d\u8bd5\u5c06 undefined \u4f5c\u4e3a\u51fd\u6570\u6267\u884c.<\/p>\n<p>\u663e\u7136\uff0cundefined <em>\u4e0d\u662f<\/em>\u4e00\u4e2a\u51fd\u6570\uff0c\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u5f97\u5230 TypeError\uff01<\/p>\n<h3>\u63d0\u5347\u51fd\u6570\u58f0\u660e<\/h3>\n<p>\u6700\u540e\uff0c\u56de\u60f3\u4e00\u4e0b\uff0c\u5728\u5b9a\u4e49 bar \u4e4b\u524d\uff0c\u6211\u4eec\u53ef\u4ee5\u8c03\u7528\u5b83\u3002\u8fd9\u662f\u7531\u4e8e<strong>\u7b2c\u4e8c\u6761\u63d0\u5347\u89c4\u5219<\/strong>\uff1a\u5f53 JavaScript \u7f16\u8bd1\u5668\u627e\u5230\u51fd\u6570\u58f0\u660e\u65f6\uff0c\u5b83\u4f1a\u4f7f\u5176\u540d\u79f0\u548c\u5b9a\u4e49\u5728\u5176\u4f5c\u7528\u57df\u7684\u9876\u90e8\u53ef\u7528\u3002<em><\/em>\u518d\u6b21\u91cd\u5199\u6211\u4eec\u7684\u4ee3\u7801\uff1a<\/p>\n<pre>function bar () {\n    if (!foo) {\n        alert(foo + \"? This is strange...\");\n    }\n    var foo = \"bar\";\n}\n\nvar broken; \/\/ undefined\n\nbar(); \/\/ bar is already defined, executes fine\n\nbroken(); \/\/ Can't execute undefined!\n\nbroken = function () {\n    alert(\"This alert won't show up!\");\n}\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u540c\u6837\uff0c\u5f53\u60a8<em>\u7f16\u5199<\/em>\u4f5c\u4e3aJavaScript<em>\u8bfb\u53d6<\/em>\u65f6\uff0c\u5b83\u66f4\u6709\u610f\u4e49\uff0c\u60a8\u4e0d\u89c9\u5f97\u5417\uff1f<\/p>\n<p>\u67e5\u770b\uff1a<\/p>\n<ol>\n<li>\u53d8\u91cf\u58f0\u660e\u548c\u51fd\u6570\u8868\u8fbe\u5f0f\u7684\u540d\u79f0\u5728\u5176\u6574\u4e2a\u8303\u56f4\u5185\u90fd\u53ef\u7528\uff0c\u4f46\u5b83\u4eec\u7684\u503c\u5728\u8d4b\u503c\u4e4b\u524d\u4e3a undefined\u3002<\/li>\n<li>\u51fd\u6570\u58f0\u660e\u7684\u540d\u79f0<em>\u200b\u200b\u548c<\/em>\u5b9a\u4e49\u5728\u5176\u6574\u4e2a\u8303\u56f4\u5185\u90fd\u53ef\u7528\uff0c<em>\u751a\u81f3\u5728<\/em>\u5176\u5b9a\u4e49\u4e4b\u524d\u3002 <\/li>\n<\/ol>\n<p>\u73b0\u5728\u8ba9\u6211\u4eec\u6765\u770b\u770b\u4e24\u4e2a\u5de5\u4f5c\u65b9\u5f0f\u7a0d\u6709\u4e0d\u540c\u7684\u65b0\u5de5\u5177\uff1alet \u548c const\u3002<\/p>\n<h3> <strong>let<\/strong><strong>\u3001<\/strong><strong><\/strong>const<strong> \u548c\u4e34\u65f6\u6b7b\u533a\u5f3a&gt;\u5f3a&gt; <\/strong> <\/h3>\n<p><strong><\/strong>\u4e0e var \u58f0\u660e\u4e0d\u540c\uff0c\u4f7f\u7528 let \u548c const \u58f0\u660e\u7684\u53d8\u91cf<em>\u4e0d<\/em>&nbsp;\u88ab\u7f16\u8bd1\u5668\u63d0\u5347\u3002<\/p>\n<p>\u81f3\u5c11\uff0c\u4e0d\u5b8c\u5168\u662f\u3002 <\/p>\n<p>\u8fd8\u8bb0\u5f97\u6211\u4eec\u5982\u4f55\u8c03\u7528 \u5df2\u635f\u574f\u7684\uff0c\u4f46\u5374\u56e0\u4e3a\u5c1d\u8bd5\u6267\u884c undefined \u800c\u6536\u5230 TypeError \u5417\uff1f\u5982\u679c\u6211\u4eec\u4f7f\u7528 let \u5b9a\u4e49 broken\uff0c\u6211\u4eec\u5c31\u4f1a\u5f97\u5230 ReferenceError\uff0c\u800c\u4e0d\u662f\uff1a<\/p>\n<pre>\"use strict\"; \n\/\/ You have to \"use strict\" to try this in Node\nbroken(); \/\/ ReferenceError!\nlet broken = function () {\n    alert(\"This alert won't show up!\");\n}\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5f53 JavaScript \u7f16\u8bd1\u5668\u5728\u7b2c\u4e00\u904d\u4e2d\u5c06\u53d8\u91cf\u6ce8\u518c\u5230\u5176\u4f5c\u7528\u57df\u65f6\uff0c\u5b83\u5bf9\u5f85 let \u548c const \u7684\u65b9\u5f0f\u4e0e\u5904\u7406 var \u7684\u65b9\u5f0f\u4e0d\u540c\u3002 <\/p>\n<\/p>\n<p>\u5f53\u5b83\u627e\u5230 var \u58f0\u660e\u65f6\uff0c\u6211\u4eec\u5c06\u8be5\u53d8\u91cf\u7684\u540d\u79f0\u6ce8\u518c\u5230\u5176\u8303\u56f4\uff0c\u5e76\u7acb\u5373\u5c06\u5176\u503c\u521d\u59cb\u5316\u4e3a undefined\u3002<\/p>\n<p>\u4f46\u662f\uff0c\u4f7f\u7528 let\uff0c\u7f16\u8bd1\u5668<em>\u4f1a<\/em>\u5c06\u53d8\u91cf\u6ce8\u518c\u5230\u5176\u4f5c\u7528\u57df\uff0c\u4f46<em>\u4e0d\u4f1a<\/em><em><\/em>\u521d\u59cb\u5316\u5176\u503c\u4e3a undefined\u3002\u76f8\u53cd\uff0c\u5b83\u4f1a\u4f7f\u53d8\u91cf\u4fdd\u6301\u672a\u521d\u59cb\u5316\u72b6\u6001\uff0c\u76f4\u5230\u5f15\u64ce\u6267\u884c\u60a8\u7684\u8d4b\u503c\u8bed\u53e5\u3002\u8bbf\u95ee\u672a\u521d\u59cb\u5316\u53d8\u91cf\u7684\u503c\u4f1a\u629b\u51fa ReferenceError\uff0c\u8fd9\u89e3\u91ca\u4e86\u4e3a\u4ec0\u4e48\u4e0a\u9762\u7684\u4ee3\u7801\u7247\u6bb5\u5728\u8fd0\u884c\u65f6\u4f1a\u629b\u51fa\u5f02\u5e38\u3002<\/p>\n<p>let \u58f0\u660e\u548c\u8d4b\u503c\u8bed\u53e5\u7684\u9876\u90e8\u5f00\u5934\u4e4b\u95f4\u7684\u7a7a\u95f4\u79f0\u4e3a\u4e34\u65f6\u6b7b\u533a\u3002\u8be5\u540d\u79f0\u6e90\u81ea\u4ee5\u4e0b\u4e8b\u5b9e\uff1a\u5373\u4f7f\u5f15\u64ce<em>\u77e5\u9053<\/em>\u540d\u4e3a foo \u7684\u53d8\u91cf\uff08\u4f4d\u4e8e bar \u8303\u56f4\u7684\u9876\u90e8\uff09\uff0c\u8be5\u53d8\u91cf\u662f\u201c\u6b7b\u7684\u201d\uff0c\u56e0\u4e3a\u5b83\u6ca1\u6709\u503c\u3002<\/p>\n<p>&#8230;\u8fd8\u56e0\u4e3a\u5982\u679c\u60a8\u5c1d\u8bd5\u5c3d\u65e9\u4f7f\u7528\u5b83\uff0c\u5b83\u4f1a\u6740\u6b7b\u60a8\u7684\u7a0b\u5e8f\u3002<\/p>\n<p>const \u5173\u952e\u5b57\u7684\u5de5\u4f5c\u65b9\u5f0f\u4e0e let \u76f8\u540c\uff0c\u4f46\u6709\u4e24\u4e2a\u4e3b\u8981\u533a\u522b\uff1a<\/p>\n<ol>\n<li>\u4f7f\u7528 const \u58f0\u660e\u65f6\uff0c<em>\u5fc5\u987b<\/em>\u5206\u914d\u4e00\u4e2a\u503c\u3002<\/li>\n<li>\u60a8<em>\u4e0d\u80fd<\/em>\u4e3a\u4f7f\u7528 const \u58f0\u660e\u7684\u53d8\u91cf\u91cd\u65b0\u8d4b\u503c\u3002<\/li>\n<\/ol>\n<p>\u8fd9\u53ef\u4ee5\u4fdd\u8bc1 const \u5c06<em>\u59cb\u7ec8<\/em><em><\/em>\u62e5\u6709\u60a8\u6700\u521d\u5206\u914d\u7ed9\u5b83\u7684\u503c\u3002<\/p>\n<pre>\/\/ This is legal\nconst React = require('react');\n\n\/\/ This is totally not legal\nconst crypto;\ncrypto = require('crypto');\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<h3> <strong>\u5757\u8303\u56f4<\/strong> <\/h3>\n<\/p>\n<p>let \u548c const \u4e0e var \u5728\u53e6\u4e00\u65b9\u9762\u6709\u6240\u4e0d\u540c\uff1a\u5b83\u4eec\u7684\u8303\u56f4\u5927\u5c0f\u3002<\/p>\n<p>\u5f53\u60a8\u4f7f\u7528 var \u58f0\u660e\u53d8\u91cf\u65f6\uff0c\u5b83\u5728\u4f5c\u7528\u57df\u94fe\u7684\u5c3d\u53ef\u80fd\u9ad8\u7684\u4f4d\u7f6e\u53ef\u89c1 &#8211; \u901a\u5e38\u662f\u5728\u6700\u8fd1\u7684\u51fd\u6570\u58f0\u660e\u7684\u9876\u90e8\uff0c\u6216\u8005\u5728\u5168\u5c40\u8303\u56f4\uff0c\u5982\u679c\u60a8\u5728\u9876\u5c42\u58f0\u660e\u5b83\u3002 <\/p>\n<p>\u4f46\u662f\uff0c\u5f53\u60a8\u4f7f\u7528 let \u6216 const \u58f0\u660e\u53d8\u91cf\u65f6\uff0c\u5b83\u4f1a\u5c3d\u53ef\u80fd<em>\u672c\u5730<\/em>\u53ef\u89c1 &#8211;<em>\u4ec5<\/em> &gt;&nbsp;\u5728\u6700\u8fd1\u7684\u8857\u533a\u5185\u3002<\/p>\n<p>\u5757\u662f\u7531\u5927\u62ec\u53f7\u5206\u9694\u7684\u4e00\u6bb5\u4ee3\u7801\uff0c\u5982 if\/else \u5757\u3001for&nbsp;\u5faa\u73af\uff0c\u4ee5\u53ca\u663e\u5f0f\u201c\u963b\u6b62\u201d\u7684\u4ee3\u7801\u5757\uff0c\u5982\u672c\u6bb5\u4ee3\u7801\u6240\u793a\u3002<\/p>\n<\/p>\n<pre>\"use strict\";\n\n{\n  let foo = \"foo\";\n  if (foo) {\n      const bar = \"bar\";\n      var foobar = foo + bar;\n\n      console.log(\"I can see \" + bar + \" in this bloc.\");\n  }\n  \n  try {\n    console.log(\"I can see \" + foo + \" in this block, but not \" + bar + \".\");\n  } catch (err) {\n    console.log(\"You got a \" + err + \".\");\n  }\n}\n\ntry {\n  console.log( foo + bar ); \/\/ Throws because of 'foo', but both are undefined\n} catch (err) {\n  console.log( \"You just got a \" + err + \".\");\n}\n\nconsole.log( foobar ); \/\/ Works fine\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5982\u679c\u60a8\u5728\u5757\u5185\u4f7f\u7528 const \u6216 let \u58f0\u660e\u53d8\u91cf\uff0c\u5219\u8be5\u53d8\u91cf<em>\u4ec5<\/em>\u5728\u5757\u5185\u53ef\u89c1\uff0c\u4e14<em>\u4ec5 \u5206\u914d\u540e\u3002<\/em><\/p>\n<\/p>\n<p>\u4f46\u662f\uff0c\u4f7f\u7528 var \u58f0\u660e\u7684\u53d8\u91cf\u5728\u5c3d\u53ef\u80fd\u8fdc\u7684\u5730\u65b9\u53ef\u89c1 &#8211; \u5728\u672c\u4f8b\u4e2d\u662f\u5728\u5168\u5c40\u8303\u56f4\u5185\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5bf9 let \u548c const \u7684\u5177\u4f53\u7ec6\u8282\u611f\u5174\u8da3\uff0c\u8bf7\u67e5\u770b Rauschmayer \u535a\u58eb\u5728\u300a\u63a2\u7d22 ES6\uff1a\u53d8\u91cf\u548c\u8303\u56f4\u300b\u4e2d\u5bf9\u5b83\u4eec\u7684\u4ecb\u7ecd\uff0c\u5e76\u67e5\u770b\u6709\u5173\u5b83\u4eec\u7684 MDN \u6587\u6863\u3002 <\/p>\n<h3>\u8bcd\u6cd5 <strong>this<\/strong> \u548c\u7bad\u5934\u51fd\u6570<\/h3>\n<p>\u4ece\u8868\u9762\u4e0a\u770b\uff0cthis \u4f3c\u4e4e\u4e0e\u8303\u56f4\u6ca1\u6709\u592a\u5927\u5173\u7cfb\u3002\u4e8b\u5b9e\u4e0a\uff0cJavaScript \u5e76\u6ca1\u6709\u6839\u636e\u6211\u4eec\u5728\u8fd9\u91cc\u8ba8\u8bba\u7684\u8303\u56f4\u89c4\u5219\u6765\u89e3\u6790 this \u7684\u542b\u4e49\u3002<\/p>\n<p>\u81f3\u5c11\uff0c\u901a\u5e38\u4e0d\u4f1a\u3002\u4f17\u6240\u5468\u77e5\uff0cJavaScript \u4e0d\u4f1a\u6839\u636e\u60a8\u4f7f\u7528\u8be5\u5173\u952e\u5b57\u7684\u4f4d\u7f6e\u6765\u89e3\u6790 this \u5173\u952e\u5b57\u7684\u542b\u4e49\uff1a<\/p>\n<pre>var foo = {\n    name: 'Foo',\n    languages: ['Spanish', 'French', 'Italian'],\n    speak : function speak () {\n        this.languages.forEach(function(language) {\n            console.log(this.name + \" speaks \" + language + \".\");\n        })\n    }\n};\n\nfoo.speak();\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u6211\u4eec\u5927\u591a\u6570\u4eba\u90fd\u8ba4\u4e3a this \u8868\u793a foo \u5728 forEach \u5faa\u73af\u5185\uff0c\u56e0\u4e3a\u8fd9\u5c31\u662f\u5b83\u5728\u5faa\u73af\u4e4b\u5916\u7684\u542b\u4e49\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u6211\u4eec\u671f\u671b JavaScript \u80fd\u591f\u89e3\u6790 this <em>\u8bcd\u6cd5<\/em>\u7684\u542b\u4e49\u3002<\/p>\n<p>\u4f46\u4e8b\u5b9e\u5e76\u975e\u5982\u6b64\u3002<\/p>\n<p>\u76f8\u53cd\uff0c\u5b83\u4f1a\u5728\u60a8\u5b9a\u4e49\u7684\u6bcf\u4e2a\u51fd\u6570\u4e2d\u521b\u5efa\u4e00\u4e2a<em>\u65b0<\/em> this\uff0c\u5e76\u6839\u636e\u60a8<em>\u5982\u4f55<\/em>\u8c03\u7528\u8be5\u51fd\u6570\u6765\u51b3\u5b9a\u5176\u542b\u4e49 -\u4e0d\u662f\u60a8\u5b9a\u4e49\u5b83\u7684<em>\u4f4d\u7f6e<\/em>\u3002<\/p>\n<p>\u7b2c\u4e00\u70b9\u7c7b\u4f3c\u4e8e\u5728\u5b50\u4f5c\u7528\u57df\u4e2d\u91cd\u65b0\u5b9a\u4e49<em>\u4efb\u4f55<\/em>\u53d8\u91cf\u7684\u60c5\u51b5\uff1a<\/p>\n<pre>function foo () {\n    var bar = \"bar\";\n    function baz () {\n        \/\/ Reusing variable names like this is called \"shadowing\" \n        var bar = \"BAR\";\n        console.log(bar); \/\/ BAR\n    }\n    baz();\n}\n\nfoo(); \/\/ BAR\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5c06 bar \u66ff\u6362\u4e3a this\uff0c\u6574\u4e2a\u4e8b\u60c5\u5e94\u8be5\u7acb\u5373\u6e05\u695a\uff01<\/p>\n<p>\u4f20\u7edf\u4e0a\uff0c\u8981\u8ba9 this \u6309\u7167\u6211\u4eec\u671f\u671b\u7684\u666e\u901a\u65e7\u8bcd\u6cd5\u8303\u56f4\u53d8\u91cf\u7684\u65b9\u5f0f\u5de5\u4f5c\uff0c\u9700\u8981\u4ee5\u4e0b\u4e24\u79cd\u89e3\u51b3\u65b9\u6cd5\u4e4b\u4e00\uff1a<\/p>\n<\/p>\n<pre>var foo = {\n    name: 'Foo',\n    languages: ['Spanish', 'French', 'Italian'],\n    speak_self : function speak_s () {\n        var self = this;\n        self.languages.forEach(function(language) {\n            console.log(self.name + \" speaks \" + language + \".\");\n        })\n    },\n    speak_bound : function speak_b () {\n        this.languages.forEach(function(language) {\n            console.log(this.name + \" speaks \" + language + \".\");\n        }.bind(foo)); \/\/ More commonly:.bind(this);\n    }\n};\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5728 speak_self \u4e2d\uff0c\u6211\u4eec\u5c06 this \u7684\u542b\u4e49\u4fdd\u5b58\u5230\u53d8\u91cf self \u4e2d\uff0c\u5e76\u4f7f\u7528\u8be5\u53d8\u91cf\u6765\u5f97\u5230\u6211\u4eec\u60f3\u8981\u7684\u53c2\u8003\u3002\u5728 speak_bound \u4e2d\uff0c\u6211\u4eec\u4f7f\u7528 bind \u6765<em>\u6c38\u4e45<\/em>\u5c06 this \u6307\u5411\u7ed9\u5b9a\u5bf9\u8c61\u3002<\/p>\n<p>ES2015 \u4e3a\u6211\u4eec\u5e26\u6765\u4e86\u4e00\u79cd\u65b0\u7684\u9009\u62e9\uff1a\u7bad\u5934\u51fd\u6570\u3002<\/p>\n<p>\u4e0e\u201c\u666e\u901a\u201d\u51fd\u6570\u4e0d\u540c\uff0c\u7bad\u5934\u51fd\u6570<em>\u4e0d\u4f1a<\/em>\u901a\u8fc7\u8bbe\u7f6e\u81ea\u5df1\u7684\u503c\u6765\u9690\u85cf\u5176\u7236\u4f5c\u7528\u57df\u7684 this \u503c\u3002\u76f8\u53cd\uff0c\u4ed6\u4eec\u4ece\u8bcd\u6c47\u4e0a\u89e3\u6790\u5176\u542b\u4e49\u3002 <\/p>\n<p>\u6362\u53e5\u8bdd\u8bf4\uff0c\u5982\u679c\u60a8\u5728\u7bad\u5934\u51fd\u6570\u4e2d\u4f7f\u7528 this\uff0cJavaScript \u4f1a\u50cf\u67e5\u627e\u4efb\u4f55\u5176\u4ed6\u53d8\u91cf\u4e00\u6837\u67e5\u627e\u5176\u503c\u3002<\/p>\n<p>\u9996\u5148\uff0c\u5b83\u68c0\u67e5\u672c\u5730\u8303\u56f4\u5185\u7684 this \u503c\u3002\u7531\u4e8e\u7bad\u5934\u51fd\u6570\u6ca1\u6709\u8bbe\u7f6e\u4e00\u4e2a\uff0c\u56e0\u6b64\u5b83\u4e0d\u4f1a\u627e\u5230\u4e00\u4e2a\u3002\u63a5\u4e0b\u6765\uff0c\u5b83\u68c0\u67e5 this \u503c\u7684<em>\u7236<\/em>\u8303\u56f4\u3002\u5982\u679c\u627e\u5230\uff0c\u5b83\u5c06\u4f7f\u7528\u5b83\u3002<\/p>\n<p>\u8fd9\u8ba9\u6211\u4eec\u53ef\u4ee5\u50cf\u8fd9\u6837\u91cd\u5199\u4e0a\u9762\u7684\u4ee3\u7801\uff1a<\/p>\n<pre>var foo = {\n    name: 'Foo',\n    languages: ['Spanish', 'French', 'Italian'],\n    speak : function speak () {\n        this.languages.forEach((language) =&amp;gt; {\n            console.log(this.name + \" speaks \" + language + \".\");\n        })\n    }\n};&nbsp;&nbsp;&nbsp;\n<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5982\u679c\u60a8\u60f3\u4e86\u89e3\u6709\u5173\u7bad\u5934\u51fd\u6570\u7684\u66f4\u591a\u8be6\u7ec6\u4fe1\u606f\uff0c\u8bf7\u67e5\u770b Envato Tuts+ \u8bb2\u5e08 Dan Wellman \u7684\u6709\u5173 JavaScript ES6 \u57fa\u7840\u77e5\u8bc6\u7684\u7cbe\u5f69\u8bfe\u7a0b\uff0c\u4ee5\u53ca\u6709\u5173\u7bad\u5934\u51fd\u6570\u7684 MDN \u6587\u6863\u3002<\/p>\n<h2>\u7ed3\u8bba<\/h2>\n<p>\u5230\u76ee\u524d\u4e3a\u6b62\uff0c\u6211\u4eec\u5df2\u7ecf\u4e86\u89e3\u4e86\u5f88\u591a\u5185\u5bb9\uff01\u5728\u672c\u6587\u4e2d\uff0c\u60a8\u4e86\u89e3\u5230\uff1a<\/p>\n<ul>\n<li>\u53d8\u91cf\u5728\u7f16\u8bd1\u671f\u95f4\u6ce8\u518c\u5230\u5176\u4f5c\u7528\u57df\uff0c\u5e76\u5728\u6267\u884c\u671f\u95f4\u4e0e\u5176\u8d4b\u503c\u76f8\u5173\u8054\u3002<\/li>\n<li>\u5728\u8d4b\u503c\u4e4b\u524d\u5f15\u7528\u4f7f\u7528<b>&nbsp;<\/b>let \u6216 class=&#8221;inline&#8221;&gt;const \u58f0\u660e\u7684\u53d8\u91cf\u4f1a\u5f15\u53d1 ReferenceError\uff0c\u5e76\u4e14\u6b64\u7c7b\u53d8\u91cf\u662f\u8303\u56f4\u5230\u6700\u8fd1\u7684\u5757\u3002<\/li>\n<li>\u7bad\u5934\u51fd\u6570<strong> <\/strong>\u5141\u8bb8\u6211\u4eec\u5b9e\u73b0 this \u7684\u8bcd\u6cd5\u7ed1\u5b9a\uff0c\u5e76\u7ed5\u8fc7\u4f20\u7edf\u7684\u52a8\u6001\u7ed1\u5b9a\u3002<\/li>\n<\/ul>\n<p>\u60a8\u8fd8\u4e86\u89e3\u4e86\u63d0\u5347\u7684\u4e24\u6761\u89c4\u5219\uff1a<\/p>\n<ul>\n<li> <strong>\u7b2c\u4e00\u6761\u63d0\u5347\u89c4\u5219<\/strong>\uff1a\u51fd\u6570\u8868\u8fbe\u5f0f\u548c var \u58f0\u660e\u5728\u5176\u5b9a\u4e49\u7684\u6574\u4e2a\u8303\u56f4\u5185\u90fd\u53ef\u7528\uff0c\u4f46\u5176\u503c\u4e3a undefined&nbsp;\u76f4\u5230\u60a8\u7684\u8d4b\u503c\u8bed\u53e5\u6267\u884c\u3002<\/li>\n<li> <strong>\u7b2c\u4e8c\u6761\u63d0\u5347\u89c4\u5219<\/strong>\uff1a\u51fd\u6570\u58f0\u660e\u7684\u540d\u79f0\u53ca\u5176\u4e3b\u4f53\u5728\u5b9a\u4e49\u5b83\u4eec\u7684\u8303\u56f4\u5185\u53ef\u7528\u3002<\/li>\n<\/ul>\n<p>\u4e0b\u4e00\u6b65\u6700\u597d\u662f\u5229\u7528 JavaScript \u4f5c\u7528\u57df\u7684\u65b0\u77e5\u8bc6\u6765\u7406\u89e3\u95ed\u5305\u3002\u4e3a\u6b64\uff0c\u8bf7\u67e5\u770b Kyle Simpson \u7684 Scopes &amp; Closures\u3002<\/p>\n<p>\u6700\u540e\uff0c\u5173\u4e8e this \u6709\u5f88\u591a\u8bdd\u8981\u8bf4\uff0c\u6211\u65e0\u6cd5\u5728\u6b64\u4ecb\u7ecd\u3002\u5982\u679c\u8be5\u5173\u952e\u5b57\u770b\u8d77\u6765\u4ecd\u7136\u50cf\u662f\u9ed1\u9b54\u6cd5\uff0c\u8bf7\u67e5\u770b\u6b64\u548c\u5bf9\u8c61\u539f\u578b\u6765\u4e86\u89e3\u5b83\u3002<\/p>\n<p>\u4e0e\u6b64\u540c\u65f6\uff0c\u5229\u7528\u60a8\u6240\u5b66\u5230\u7684\u77e5\u8bc6\u5e76\u51cf\u5c11\u7f16\u5199\u9519\u8bef\uff01<\/p>\n<p><strong>\u5b66\u4e60 JavaScript\uff1a\u5b8c\u6574\u6307\u5357<\/strong><\/p>\n<p>\u6211\u4eec\u6784\u5efa\u4e86\u4e00\u4e2a\u5b8c\u6574\u7684\u6307\u5357\u6765\u5e2e\u52a9\u60a8\u5b66\u4e60 JavaScript\uff0c\u65e0\u8bba\u60a8\u662f\u521a\u521a\u5f00\u59cb\u4f5c\u4e3a Web \u5f00\u53d1\u4eba\u5458\u8fd8\u662f\u60f3\u63a2\u7d22\u66f4\u9ad8\u7ea7\u7684\u4e3b\u9898\u3002<\/p>\n<p>\u4ee5\u4e0a\u5c31\u662f\u7406\u89e3JavaScript\u4e2d\u7684\u4f5c\u7528\u57df\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u8303\u56f4\uff0c\u6216\u786e\u5b9a\u53d8\u91cf\u6240\u5728\u4f4d\u7f6e\u7684\u4e00\u7ec4\u89c4\u5219\uff0c\u662f\u4efb\u4f55\u7f16\u7a0b\u8bed\u8a00\u7684\u6700\u57fa\u672c\u6982\u5ff5\u4e4b\u4e00\u3002\u4e8b\u5b9e\u4e0a\uff0c\u5b83\u662f\u5982\u6b64\u57fa\u672c\uff0c\u4ee5\u81f3\u4e8e\u6211\u4eec\u5f88\u5bb9\u6613\u5fd8\u8bb0\u8fd9\u4e9b\u89c4\u5219\u662f\u591a\u4e48\u5fae\u5999\uff01 \u51c6\u786e\u7406\u89e3 JavaScript \u5f15\u64ce\u5982\u4f55\u201c\u601d\u8003\u201d\u4f5c\u7528\u57df\u5c06\u4f7f\u60a8\u907f\u514d\u7f16\u5199\u63d0\u5347\u53ef\u80fd\u5bfc\u81f4\u7684\u5e38\u89c1\u9519\u8bef\uff0c\u8ba9\u60a8\u505a\u597d\u51c6\u5907\u4e13\u6ce8\u4e8e\u95ed\u5305\uff0c\u5e76\u8ba9\u60a8\u79bb\u6c38\u8fdc\u4e0d\u518d\u7f16\u5199\u9519\u8bef\u66f4\u8fd1\u4e00\u6b65 \u518d\u6b21\u3002 &#8230;\u65e0\u8bba\u5982\u4f55\uff0c\u5b83\u4f1a\u5e2e\u52a9\u60a8\u7406\u89e3\u63d0\u5347\u548c\u5173\u95ed\u3002 \u5728\u672c\u6587\u4e2d\uff0c\u6211\u4eec\u5c06\u4e86\u89e3\uff1a \u7acb\u5373\u5b66\u4e60\u201c\u201d\uff1b JavaScript \u4e2d\u4f5c\u7528\u57df\u7684\u57fa\u7840\u77e5\u8bc6 \u89e3\u91ca\u5668\u5982\u4f55\u51b3\u5b9a\u54ea\u4e9b\u53d8\u91cf\u5c5e\u4e8e\u54ea\u4e2a\u4f5c\u7528\u57df \u540a\u88c5\u7684\u5b9e\u9645\u5de5\u4f5c\u539f\u7406 ES6 \u5173\u952e\u5b57 let \u548c const \u5982\u4f55\u6539\u53d8\u6e38\u620f\u89c4\u5219 \u8ba9\u6211\u4eec\u6df1\u5165\u63a2\u8ba8\u3002 \u5982\u679c\u60a8\u6709\u5174\u8da3\u4e86\u89e3\u6709\u5173 ES6 \u7684\u66f4\u591a\u4fe1\u606f\u4ee5\u53ca\u5982\u4f55\u5229\u7528\u8bed\u6cd5\u548c\u529f\u80fd\u6765\u6539\u8fdb\u548c\u7b80\u5316 JavaScript \u4ee3\u7801\uff0c\u4e3a\u4ec0\u4e48\u4e0d\u770b\u770b\u8fd9\u4e24\u95e8\u8bfe\u7a0b\uff1a \u8bcd\u6cd5\u8303\u56f4 \u5982\u679c\u60a8\u4e4b\u524d\u7f16\u5199\u8fc7\u4e00\u884c JavaScript\uff0c\u60a8\u5c31\u4f1a\u77e5\u9053\u5b9a\u4e49\u53d8\u91cf\u7684\u4f4d\u7f6e\u51b3\u5b9a\u4e86\u60a8\u53ef\u4ee5\u4f7f\u7528\u7684\u4f4d\u7f6e&gt; \u4ed6\u4eec\u3002\u53d8\u91cf\u7684\u53ef\u89c1\u6027\u53d6\u51b3\u4e8e\u6e90\u4ee3\u7801\u7684\u7ed3\u6784\uff0c\u8fd9\u4e00\u4e8b\u5b9e\u79f0\u4e3a\u8bcd\u6cd5 \u8303\u56f4\u3002 \u5728 JavaScript \u4e2d\u521b\u5efa\u4f5c\u7528\u57df\u6709\u4e09\u79cd\u65b9\u6cd5\uff1a \u521b\u5efa\u51fd\u6570\u3002\u5728\u51fd\u6570\u5185\u90e8\u58f0\u660e\u7684\u53d8\u91cf\u4ec5\u5728\u8be5\u51fd\u6570\u5185\u90e8\u53ef\u89c1\uff0c\u5305\u62ec\u5728\u5d4c\u5957\u51fd\u6570\u4e2d\u3002 \u4f7f\u7528 let \u6216 const \u5728\u4ee3\u7801\u5757\u5185\u58f0\u660e\u53d8\u91cf\u3002\u6b64\u7c7b\u58f0\u660e\u4ec5\u5728\u5757\u5185\u53ef\u89c1\u3002 \u521b\u5efacatch \u5757\u3002\u4e0d\u7ba1\u4f60\u76f8\u4fe1\u4e0e\u5426\uff0c\u8fd9\u5b9e\u9645\u4e0a\u786e\u5b9e\u521b\u5efa\u4e86\u4e00\u4e2a\u65b0\u7684\u8303\u56f4\uff01 &#8220;use strict&#8221;; var mr_global = &#8220;Mr Global&#8221;; function foo () { var mrs_local = &#8220;Mrs [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18],"tags":[],"class_list":["post-32426","post","type-post","status-publish","format-standard","hentry","category-cms"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/32426","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=32426"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/32426\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=32426"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=32426"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=32426"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}