Why Are Two Identical JavaScript Objects Not Considered Equal?

Understanding Object Equality: Why Two Identical Objects Are Not Equal

In programming, it is intuitive to assume that two variables representing identical objects should be considered equal. However, in JavaScript, comparing two objects using the equality operator (==) or strict equality operator (===) often yields surprising results.

The Mystery: Non-Equal Identical Objects

Consider the following code:

var a = {};
var b = {};

console.log(a == b); //returns false
console.log(a === b); //returns false

Instead of returning true as expected, both comparisons return false. This behavior confuses developers who expect two seemingly identical objects to be equal.

The Explanation: Object Comparison Semantics

The key to understanding this behavior lies in the way JavaScript compares objects. Unlike primitive data types like numbers or strings, objects have their own unique identity or reference. When comparing two objects, the equality operators check if they refer to the same exact object.

Identity vs. Value

In the example above, a and b are two distinct objects, even though they have the same structure and properties. Each object has its own unique reference, and the equality operators are evaluating this reference instead of the object's value.

Implications for Object Comparison

This behavior has significant implications for object comparison. Two objects will only be equal if they refer to the same exact object. Assigning one object to another simply creates a new reference to the same object.

Workaround: Comparing Object Properties

If you need to compare the equality of two objects' properties, one workaround is to use the JSON.stringify() method to convert the objects to JSON strings and then compare the resulting strings. Alternatively, you can use a helper function or library to recursively compare object properties.

The above is the detailed content of Why Are Two Identical JavaScript Objects Not Considered Equal?. For more information, please follow other related articles on the PHP Chinese website!