A JavaScript object is a complex data type that can contain various data types. For example,
const person = {
name: 'John',
age: 21,
}
Here, person
is an object. Now, you can't clone an object by doing something like this.
const copy = person;
console.log(copy); // {name: "John", age: 21}
In the above program, the copy
variable has the same value as the person
object. However, if you change the value of the copy
object, the value in the person
object will also change. For example,
copy.name = 'Peter';
console.log(copy.name); // Peter
console.log(person.name); // Peter
The change is seen in both objects because objects are reference types. And both copy
and person
are pointing to the same object.
Example 1. Clone the Object Using Object.assign()
// program to clone the object
// declaring object
const person = {
name: 'John',
age: 21,
}
// cloning the object
const clonePerson = Object.assign({}, person);
console.log(clonePerson);
// changing the value of clonePerson
clonePerson.name = 'Peter';
console.log(clonePerson.name);
console.log(person.name);
Output
{name: "John", age: 21} Peter John
The Object.assign()
method is part of the ES6 standard. The Object.assign()
method performs deep copy and copies all the properties from one or more objects.
Note: The empty {}
as the first argument ensures that you don't change the original object.
Example 2: Clone the Object Using Spread Syntax
// program to clone the object
// declaring object
const person = {
name: 'John',
age: 21,
}
// cloning the object
const clonePerson = { ... person}
console.log(clonePerson);
// changing the value of clonePerson
clonePerson.name = 'Peter';
console.log(clonePerson.name);
console.log(person.name);
Output
{name: "John", age: 21} Peter John
The spread syntax ...
was introduced in the later version(ES6).
The spread syntax can be used to make a shallow copy of an object. This means it will copy the object. However, the deeper objects are referenced. For example,
const person = {
name: 'John',
age: 21,
// the inner objects will change in the shallow copy
marks: { math: 66, english: 73}
}
// cloning the object
const clonePerson = { ... person}
console.log(clonePerson); // {name: "John", age: 21, marks: {…}}
// changing the value of clonePerson
clonePerson.marks.math = 100;
console.log(clonePerson.marks.math); // 100
console.log(person.marks.math); // 100
Here, when the inner object value math
is changed to 100 of clonePerson
object, the value of the math
key of the person
object also changes.
Example 3: Clone the Object Using JSON.parse()
// program to clone the object
// declaring object
const person = {
name: 'John',
age: 21,
}
// cloning the object
const clonePerson = JSON.parse(JSON.stringify(person));
console.log(clonePerson);
// changing the value of clonePerson
clonePerson.name = 'Peter';
console.log(clonePerson.name);
console.log(person.name);
Output
{name: "John", age: 21} Peter John
In the above program, the JSON.parse()
method is used to clone an object.
Note: JSON.parse()
only works with Number
and String
object literal. It does not work with an object literal with function
or symbol
properties.
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