In JavaScript, garbage collection (Garbage Collection) is an automatic memory management mechanism that is responsible for detecting and recycling objects that are no longer used in order to free up memory space for use by other objects. This article will introduce the garbage collection mechanism of JavaScript in detail and provide corresponding source code examples.
The garbage collection mechanism in JavaScript mainly relies on two core concepts: reference counting and mark cleaning.
- Reference Counting: This is a simple garbage collection algorithm that determines whether to recycle each object by tracking the number of times it has been referenced. When the object is created, the reference count is 1. Whenever a reference points to the object, the reference count is incremented by 1; when the reference expires or is assigned another value, the reference count is decremented by 1. When the reference count is 0, it means that the object is no longer referenced and can be recycled.
However, there is a problem with the reference counting algorithm, namely circular references. When two or more objects reference each other, their reference counts never reach 0, causing a memory leak. To solve this problem, the JavaScript engine introduced the mark-and-sweep algorithm.
- Mark and Sweep: The mark and sweep algorithm uses the root object (usually the global object) as the starting point, traverses the reference relationship of the object, and marks all accessible objects. After the marking phase ends, unmarked objects are inaccessible garbage objects and can be recycled.
Here is a sample code that demonstrates the garbage collection process in JavaScript:
// 创建对象
let obj1