jQuery源代码中的奇怪代码：var！== var？ x：y;

本文介绍了jQuery源代码中的奇怪代码：var！== var？ x：y;的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 限时删除！！ 最近我在jQuery源代码中发现了一个奇怪的行（最新版本1.9.1，Sizzle包，第129行 funescape 函数）：Recently I found one weird line in the jQuery sources (last version 1.9.1, Sizzle package, line 129 funescape function):funescape = function( _, escaped ) { var high = "0x" + escaped - 0x10000; // NaN means non-codepoint return high !== high ? // <--- LINE 129 escaped : // BMP codepoint high < 0 ? String.fromCharCode( high + 0x10000 ) : // Supplemental Plane codepoint (surrogate pair) String.fromCharCode( high >> 10 | 0xD800, high & 0x3FF | 0xDC00 );};使高的原因是什么？==高比较？它显然看起来像返回转义永远不会被执行。或者我会错过什么？What is the reason to make high !== high comparison? It obviously looks like return escaped will never be executed. Or do I miss something? 参考： https://github.com/jquery/sizzle/blob/master/sizzle.js#L129推荐答案事实上它写在上面的评论中：In fact it is written in the comment right above:因此必须先执行此比较以处理 NaN 在JavaScript中的情况：So it is mandatory to perform this comparison first to handle the NaN case as in JavaScript: NaN === NaN 返回 false 。正如 James Wiseman所指出的同样重要的是要知道为什么开发人员使用 high！== high 而不是 isNaN（高）哪个会更清楚。As pointed out by James Wiseman it is also important to know why the developer used high !== high instead of isNaN(high) which would have been clearer.这肯定是基于表现。 测试显示 a！== a 比 isNaN（a） 快20倍。It is certainly based on performance. This test shows that a !== a is twenty times faster than isNaN(a). zzzzBov 还表示可以使用 isNaN（） c $ c>！== 也更便携。zzzzBov also indicates that isNaN() could be overwritten, using !== is also more portable.来自 Benjamin Gruenbaum ：并且来自 Jan Dvorak ： 这篇关于jQuery源代码中的奇怪代码：var！== var？ x：y;的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 1403页，肝出来的..