問題描述

這樣可以嗎?:

function mygetTime()
{
    var d = new Date();
    return(d.getTime());
}

function wasteSomeMemory()
{
    var temp;
    for(var count = 0; count < 1000000; count += 1)
    {
        temp = mygetTime();
    }
}

調用 wasteSomeMemory() 會導致內存泄漏嗎?

Will calling wasteSomeMemory() cause a memory leak?

這個呢:

function wasteSomeMemory2()
{
    var temp;
    for(var count = 0; count < 1000000; count += 1)
    {
        temp = new Date();
    }
}

調用 wasteSomeMemory2() 會導致內存泄漏嗎?我應該在 for 循環的末尾使用 delete temp; 嗎?

Will calling wasteSomeMemory2() cause a memory leak? Should I use delete temp; at the end of the for-loop?

function wasteSomeMemory2()
{
    var temp;
    for(var count = 0; count < 1000000; count += 1)
    {
        temp = new Date();
        delete temp;
    }
}

推薦答案

new 和 delete 在 JavaScript 中彼此沒有任何關系(盡管它們與其他語言中完全不同的結構).不要擔心在沒有明確清理的情況下創建對象(new)，這是垃圾收集器的工作.

new and delete have nothing whatsoever to do with each other in JavaScript (despite their confusing similarity to completely different constructs in other languages). Don't worry about creating objects (new) without explicitly cleaning them up, that's the garbage collector's job.

new 用于通過構造函數創建對象.另一方面，delete 用于從對象中刪除屬性.它與從內存中刪除對象無關，除了作為副作用(例如，如果對該對象的唯一未完成引用來自您刪除的屬性).

new is for creating objects via constructor functions. delete, on the other hand, is for removing properties from objects. It has nothing to do with removing an object from memory, other than as a side effect (e.g., if the only outstanding reference to that object was from the property that you removed).

delete的正確使用示例:

var obj = {};
obj.foo = "bar"; // Now `obj` has a property called `foo`
delete obj.foo;  // Now it doesn't

您的 getmyTime 功能非常好.Date 對象將有資格在函數返回后立即被回收(是否被回收完全取決于實現).它不會導致內存泄漏，除非有錯誤的實現.

Your getmyTime function is perfectly fine. The Date object will become eligible to be reclaimed immediately upon function return (whether it is reclaimed is completely down to the implementation). It does not cause a memory leak, except on a buggy implementation.

您的 wasteSomeMemory2 同樣不會導致內存泄漏，實際上您不能調用 delete temp; —你只能刪除屬性，不能刪除變量.

Your wasteSomeMemory2 similarly doesn't cause a memory leak, and in fact you can't call delete temp; — you can only delete properties, not vars.

有 次您必須幫助垃圾收集器，但這些通常(根據我的經驗)與對象屬性無關，因此不涉及 delete.它們只有在您創建函數實例時才會真正出現(如果您正在設置事件處理程序或計時器函數等，這很常見).例如，考慮:

function foo() {
    var listOfThings = /* ...get a list of things... */;

    // ...do something with `listOfThings`...

    setInterval(function() {
       // ...do something that *doesn't* need `listOfThings`...
    }, 1000);
}

function foo() {

    var listOfThings = /* ...get a list of things... */;

    // ...do something with `listOfThings`...

    listOfThings = undefined; // Done with it           <== The new bit

    setInterval(function() {
       // ...do something that *doesn't* need `listOfThings`...
    }, 1000);
}