Introduction to the difference between deep copy and shallow copy in JavaScript

This article brings you an introduction to the difference between deep copy and shallow copy in JavaScript. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

This article explains the difference between deep copy and shallow copy in JavaScript.

Shallow Copy/Shallow Copy

Shallow copy refers to copying the reference value.

var original = {"prop1" : "Prop1", "prop2" : "prop2"};
console.log(JSON.stringify(original));
// {"prop1" : "Prop1", "prop2" : "prop2"}

var shallowCopy = original;
console.log(JSON.stringify(shallowCopy));
// {"prop1" : "Prop1", "prop2" : "prop2"}

shallowCopy.prop1 = "ChangedProp1";

console.log(JSON.stringify(original));
// {"prop1" : "ChangedProp1", "prop2" : "prop2"}
console.log(JSON.stringify(shallowCopy));
// {"prop1" : "ChangedProp1", "prop2" : "prop2"}

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Note:

• In a shallow copy, the original value and the copy share the same attributes.

• Shallow copy only copies the object reference.

• In shallow copy, if the copied object is modified, it will affect the original object, and vice versa.

• In js, the assignment of arrays and objects defaults to shallow copy.

Deep Copy

Deep copy refers to recursively copying the properties of an object to a new object. In jquery we use $.extend to perform deep copy.

$.extend(deepCopy, target, object1, [objectN] )

The first parameter is passed in true, indicating that this is a deep copy, target is the target object, object1, the original object.

var original = {"prop1" : "Prop1", "prop2" : "prop2"};
console.log(JSON.stringify(original));
// {"prop1" : "Prop1", "prop2" : "prop2"}

var deepCopy = $.extend(true, {}, original);
console.log(JSON.stringify(deepCopy));
// {"prop1" : "Prop1", "prop2" : "prop2"}

deepCopy.prop1 = "ChangedProp1";

console.log(JSON.stringify(original));
// {"prop1" : "Prop1", "prop2" : "prop2"}
console.log(JSON.stringify(deepCopy));
// {"prop1" : "ChangedProp1", "prop2" : "prop2"}

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• In deep copy, the copy and the original object do not share attributes

• Deep copy recursive copy attributes

• The copy of the deep copy will not affect the original object, and vice versa

• All primitive data types in js perform deep copy by default, such as Boolean, null, Undefined, Number, String, etc.

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