Question
Answer and Explanation
The Object.assign() method in JavaScript is a powerful tool used to copy the values of all enumerable own properties from one or more source objects to a target object. It returns the modified target object. This method is particularly useful for merging objects, creating shallow copies, and setting default values.
Here's a breakdown of how it works:
Syntax:
Object.assign(target, ...sources)
Where:
- `target`: The target object to which properties will be copied. This object will be modified.
- `sources`: One or more source objects from which properties will be copied. These objects are not modified.
Key Characteristics:
- Shallow Copy: Object.assign() performs a shallow copy. This means that if a property value is an object itself, only the reference to that object is copied, not the object itself. Changes to nested objects in the copied object will affect the original object and vice versa.
- Enumerable Own Properties: It only copies enumerable own properties. Properties inherited from the prototype chain or non-enumerable properties are not copied.
- Overwriting Properties: If a property with the same name exists in multiple source objects, the property from the later source object will overwrite the property from the earlier source object.
- Returns Modified Target: The method returns the modified target object, which can be useful for chaining operations.
Example:
const target = { a: 1, b: 2 };
const source1 = { b: 3, c: 4 };
const source2 = { d: 5 };
const returnedTarget = Object.assign(target, source1, source2);
console.log(target); // Output: { a: 1, b: 3, c: 4, d: 5 }
console.log(returnedTarget === target); // Output: true
In this example, the properties from `source1` and `source2` are copied to `target`. The property `b` from `source1` overwrites the original `b` in `target`. The method returns the modified `target` object.
Use Cases:
- Merging Objects: Combining multiple objects into a single object.
- Creating Shallow Copies: Creating a new object with the same properties as an existing object (though nested objects are still references).
- Setting Default Values: Providing default values for an object by merging it with an object containing default properties.
Important Note:
For deep copies (copying nested objects), you would need to use other methods like recursion or libraries that provide deep copy functionality, as Object.assign() only performs a shallow copy.
In summary, Object.assign() is a versatile method for manipulating objects in JavaScript, particularly useful for merging, shallow copying, and setting default values. Understanding its behavior, especially its shallow copy nature, is crucial for effective use.