当涉及到DOM对象时，要注意循环引用:

JavaScript中的内存泄漏模式

请记住，只有在没有对对象的活动引用时才能回收内存。这是闭包和事件处理程序的一个常见陷阱，因为一些JS引擎不会检查内部函数中实际引用了哪些变量，而只是保留封闭函数的所有局部变量。

这里有一个简单的例子:

function init() {
    var bigString = new Array(1000).join('xxx');
    var foo = document.getElementById('foo');
    foo.onclick = function() {
        // this might create a closure over `bigString`,
        // even if `bigString` isn't referenced anywhere!
    };
}

只要事件处理程序存在，简单的JS实现就不能收集bigString。有几种方法可以解决这个问题，例如在init()末尾设置bigString = null (delete对局部变量和函数参数不起作用:delete将从对象中删除属性，并且变量对象不可访问-如果您试图删除局部变量，ES5在严格模式下甚至会抛出ReferenceError !)

如果您关心内存消耗，我建议尽可能避免不必要的闭包。

当涉及到DOM对象时，要注意循环引用:

JavaScript中的内存泄漏模式

请记住，只有在没有对对象的活动引用时才能回收内存。这是闭包和事件处理程序的一个常见陷阱，因为一些JS引擎不会检查内部函数中实际引用了哪些变量，而只是保留封闭函数的所有局部变量。

这里有一个简单的例子:

function init() {
    var bigString = new Array(1000).join('xxx');
    var foo = document.getElementById('foo');
    foo.onclick = function() {
        // this might create a closure over `bigString`,
        // even if `bigString` isn't referenced anywhere!
    };
}

只要事件处理程序存在，简单的JS实现就不能收集bigString。有几种方法可以解决这个问题，例如在init()末尾设置bigString = null (delete对局部变量和函数参数不起作用:delete将从对象中删除属性，并且变量对象不可访问-如果您试图删除局部变量，ES5在严格模式下甚至会抛出ReferenceError !)

如果您关心内存消耗，我建议尽可能避免不必要的闭包。

Eric Lippert wrote a detailed blog post about this subject a while back (additionally comparing it to VBScript). More accurately, he wrote about JScript, which is Microsoft's own implementation of ECMAScript, although very similar to JavaScript. I would imagine that you can assume the vast majority of behaviour would be the same for the JavaScript engine of Internet Explorer. Of course, the implementation will vary from browser to browser, though I suspect you could take a number of the common principles and apply them to other browsers.

引自该页:

JScript uses a nongenerational mark-and-sweep garbage collector. It works like this: Every variable which is "in scope" is called a "scavenger". A scavenger may refer to a number, an object, a string, whatever. We maintain a list of scavengers -- variables are moved on to the scav list when they come into scope and off the scav list when they go out of scope. Every now and then the garbage collector runs. First it puts a "mark" on every object, variable, string, etc – all the memory tracked by the GC. (JScript uses the VARIANT data structure internally and there are plenty of extra unused bits in that structure, so we just set one of them.) Second, it clears the mark on the scavengers and the transitive closure of scavenger references. So if a scavenger object references a nonscavenger object then we clear the bits on the nonscavenger, and on everything that it refers to. (I am using the word "closure" in a different sense than in my earlier post.) At this point we know that all the memory still marked is allocated memory which cannot be reached by any path from any in-scope variable. All of those objects are instructed to tear themselves down, which destroys any circular references.

垃圾收集的主要目的是让程序员不必担心他们创建和使用的对象的内存管理问题，当然有时无法避免——至少对垃圾收集的工作方式有一个粗略的了解总是有益的。

历史注释:答案的早期修订对delete操作符的引用不正确。在JavaScript中，delete操作符从对象中删除一个属性，这与C/ c++中的delete完全不同。

什么是JavaScript垃圾收集?

检查这个

对于web程序员来说，了解JavaScript垃圾收集的重要一点是， 为了写出更好的代码?

在Javascript中，你不关心内存分配和释放。整个问题都需要Javascript解释器来解决。在Javascript中泄漏仍然是可能的，但它们是解释器的错误。如果你对这个话题感兴趣，你可以阅读更多 www.memorymanagement.org

引用类型不将对象直接存储到变量中 它被赋值了，下面例子中的对象变量，实际上没有 包含对象实例。相反，它持有指向的指针(或引用) 内存中对象存在的位置。

var object = new Object();

如果将一个引用类型变量赋值给另一个引用类型变量，则每个变量 获取指针的副本，两者仍然引用中相同的对象 内存。

var object1 = new Object();
var object2 = object1;

JavaScript是一种垃圾收集语言，所以实际上不需要这样做 使用引用类型时，要考虑内存分配问题。然而, 最好取消对不再需要的对象的引用，以便垃圾 收集器可以释放该内存。最好的方法是设置 对象变量为null。

var object1 = new Object();
// do something
object1 = null; // dereference

在使用数百万个对象的大型应用程序中，取消引用对象尤其重要。

摘自《面向对象的JavaScript原则》——NICHOLAS C. ZAKAS

据我所知，JavaScript的对象在没有对对象的引用时周期性地进行垃圾收集。这是自动发生的事情，但如果你想了解更多关于它是如何工作的，在c++级别，看一看WebKit或V8源代码是有意义的

Typically you don't need to think about it, however, in older browsers, like IE 5.5 and early versions of IE 6, and perhaps current versions, closures would create circular references that when unchecked would end up eating up memory. In the particular case that I mean about closures, it was when you added a JavaScript reference to a dom object, and an object to a DOM object that referred back to the JavaScript object. Basically it could never be collected, and would eventually cause the OS to become unstable in test apps that looped to create crashes. In practice these leaks are usually small, but to keep your code clean you should delete the JavaScript reference to the DOM object.

通常，使用delete关键字立即取消对JSON数据等大对象的引用是一个好主意，特别是在移动web开发中。这将导致GC的下一次扫描删除该对象并释放其内存。