这种非标准的方式已经在40的版本之后被移除了. 现在开始它会在控制台里抛出一个SyntaxError("for-in loop head declarations may not have initializers") 警告。(bug 748550以及bug 1164741)。 像其他引擎 V8(Chrome),Chakra (IE/Edge), JSC (WebKit/Safari) 正在研究去除这种不标准的行为。
MDN上的定义: 在可迭代对象(包括 Array,Map,Set,String,TypedArray,arguments 对象等等)上创建一个迭代循环,调用自定义迭代钩子,并为每个不同属性的值执行语句。 可以看到它支持的种类非常多,最常用的就是Array和arguments了,但是注意虽然支持这么多并不能像for...in...用于普通Object的迭代。上面我们不推荐for......
属性arrCustom和objCustom没有被打印,因为它们是继承属性。 for...of循环迭代并打印iterable按照数组(数组是可迭代的)定义要进行迭代的值。对象的元素3、5、7被打印,但对象的属性没有被打印。 Specification ECMAScript® 2026 Language Specification #sec-for-in-and-for-of-statements...
arrfor(letl=0,r=arr.length-1;l<r;l++,r--){console.log(arr[l],arr[r]);}// 1 6// 2 5// 3 4 Specification ECMAScript® 2026 Language Specification #sec-for-statement 参见 空语句 break continue while do...while for...in ...
The index value is a popular interface within any loop iteration (whether for or while) that can help access the elements within an iterable or sequences (e.g., array) which can be elusive for certain loop types. In JavaScript, the for loop can be achieved in different ways - for, for...
JavaScriptfor :http://www.runoob.com/js/js-loop-for.html JavaScriptfor/in :http://www.runoob.com/jsref/jsref-forin.html MDN - for...of :https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Statements/for...of Javascript statement :http://www.runoob.com/jsref/jsref-stat...
Simplified Syntax:Thefor-await-ofloop makes consuming async iterators straightforward. On-Demand Data Fetching:Fetch only the data you need, reducing memory usage and load on the backend. Future Compatibility:Async iterators are a standard feature in JavaScript, ensuring compatibility with future updates...
根据 MDN 的描述,every 在返回 true 的情况下继续循环,返回 false 的情况下中断执行。那我们就先来模拟下 break const arr = [1, 2, 3, 4] arr.every(item => { if (item === 3) { return false } return true }) 再来模拟下 continue const arr = [1, 2, 3, 4] arr.every(item => ...
[1]From Chrome 29 to Chrome 37 this feature was available behind a preference. In chrome://flags/#enable-javascript-harmony, activate the entry “Enable Experimental JavaScript”. [2]Prior Firefox 51, using thefor...ofloop construct with theconstkeyword threw aSyntaxError("missing = in const...
以下代码中的搜索函数不起作用,我认为这与For...In循环有关,但我是JS新手,不确定原因: 代码语言:javascript 运行 AI代码解释 var friends = { bill: { firstName: "bill", lastName: "smith", number: 1, address: ["1"] }, steve: { firstName: "steve", lastName: "smith", number: 2, addre...