JavaScript、Node.js:Array.forEach 是异步的吗? [英] JavaScript, Node.js: is Array.forEach asynchronous?
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问题描述
我有一个关于 JavaScript 的原生 Array.forEach
实现的问题:它的行为是异步的吗?例如,如果我调用:
I have a question regarding the native Array.forEach
implementation of JavaScript: Does it behave asynchronously?
For example, if I call:
[many many elements].forEach(function () {lots of work to do})
这会是非阻塞的吗?
推荐答案
不,它正在阻塞.查看算法规范.
No, it is blocking. Have a look at the specification of the algorithm.
然而,在 MDN:
if (!Array.prototype.forEach)
{
Array.prototype.forEach = function(fun /*, thisp */)
{
"use strict";
if (this === void 0 || this === null)
throw new TypeError();
var t = Object(this);
var len = t.length >>> 0;
if (typeof fun !== "function")
throw new TypeError();
var thisp = arguments[1];
for (var i = 0; i < len; i++)
{
if (i in t)
fun.call(thisp, t[i], i, t);
}
};
}
<小时>
如果你必须为每个元素执行大量代码,你应该考虑使用不同的方法:
If you have to execute a lot of code for each element, you should consider to use a different approach:
function processArray(items, process) {
var todo = items.concat();
setTimeout(function() {
process(todo.shift());
if(todo.length > 0) {
setTimeout(arguments.callee, 25);
}
}, 25);
}
然后调用它:
processArray([many many elements], function () {lots of work to do});
这将是非阻塞的.该示例取自 高性能 JavaScript.
This would be non-blocking then. The example is taken from High Performance JavaScript.
另一个选项可能是网络工作者.
Another option might be web workers.
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