Что такое сборка "мусора" JavaScript?

Остерегайтесь циклических ссылок, когда задействованы объекты DOM:

Шаблоны утечки памяти в JavaScript

Помните, что память может быть освобождена только при отсутствии активных ссылок на объект. Это обычная ошибка с замыканиями и обработчиками событий, так как некоторые JS-движки не проверяют, на какие переменные на самом деле ссылаются во внутренних функциях, а просто сохраняют все локальные переменные включающих функций.

Вот простой пример:

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!
    };
}

Наивный Реализация JS не может собирать bigString , пока есть обработчик событий. Есть несколько способов решить эту проблему, например, установка bigString = null в конце init () ( delete не будет работать для локальных переменных и функции аргументы:

Good quote taken from a blog

The DOM component is "garbage collected", as is the JScript component, which means that if you create an object within either component, and then lose track of that object, it will eventually be cleaned up.

For example:

function makeABigObject() {
var bigArray = new Array(20000);
}

When you call that function, the JScript component creates an object (named bigArray) that is accessible within the function. As soon as the function returns, though, you "lose track" of bigArray because there's no way to refer to it anymore. Well, the JScript component realizes that you've lost track of it, and so bigArray is cleaned up--its memory is reclaimed. The same sort of thing works in the DOM component. If you say document.createElement('div'), or something similar, then the DOM component creates an object for you. Once you lose track of that object somehow, the DOM component will clean up the related.

To the best of my knowledge, JavaScript's objects are garbage collected periodically when there are no references remaining to the object. It is something that happens automatically, but if you want to see more about how it works, at the C++ level, it makes sense to take a look at the WebKit or V8 source code

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.

Usually it is a good idea to use the delete keyword to immediately de-reference big objects like JSON data that you have received back and done whatever you need to do with it, especially in mobile web development. This causes the next sweep of the GC to remove that object and free its memory.

"In computer science, garbage collection (GC) is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory used by objects that will never be accessed or mutated again by the application."

All JavaScript engines have their own garbage collectors, and they may differ. Most time you do not have to deal with them because they just do what they supposed to do.

Writing better code mostly depends of how good do you know programming principles, language and particular implementation.

Что такое сборка мусора JavaScript?

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Что важно для веб-программиста о сборке мусора в JavaScript, для написания лучшего кода?

В Javascript вы не заботитесь о распределении и освобождении памяти. Вся проблема возложена на интерпретатор Javascript. В Javascript по-прежнему возможны утечки, но это ошибки интерпретатора. Если вам интересна эта тема, вы можете прочитать больше в www.memorymanagement.org