The difference between concat and push in JS

The difference between concat and push in Js: 1. concat is used to merge two or more arrays into a new array and return this new array, while push is used to add one or more arrays to the end of the array. elements, and returns the new length of the modified array; 2. concat will not modify the original array, but will create a new array, while push will modify the original array and add new elements to the end of the original array; 3. concat can be used It is suitable for merging any number of arrays, and can also be used to merge arrays and other types of values, etc.

In JavaScript, `concat` and `push` are two commonly used methods in array operations. They have some differences and different uses.

First, the `concat` method is used to merge two or more arrays into a new array and return this new array. The `concat` method does not modify the original array, but creates a new array. For example:

let arr1 = [1, 2, 3];
let arr2 = [4, 5, 6];
let newArr = arr1.concat(arr2);
console.log(newArr); // [1, 2, 3, 4, 5, 6]
console.log(arr1); // [1, 2, 3]
console.log(arr2); // [4, 5, 6]

You can see that the `concat` method merges `arr1` and `arr2` into a new array `newArr`, while the original `arr1` and `arr2` arrays have not changed. .

Secondly, the `push` method is used to add one or more elements to the end of the array and return the new length of the modified array. The `push` method modifies the original array, adding new elements to the end of the original array. For example:

let arr = [1, 2, 3];
let length = arr.push(4, 5, 6);
console.log(arr); // [1, 2, 3, 4, 5, 6]
console.log(length); // 6

You can see that the `push` method adds new elements `4, 5, 6` to the end of the `arr` array and returns the new length of the modified array.

In addition, the `concat` method can be used to merge any number of arrays, and can also be used to merge arrays and other types of values. For example:

let arr1 = [1, 2, 3];
let arr2 = [4, 5, 6];
let newArr = arr1.concat(arr2, 7, 8, "nine");
console.log(newArr); // [1, 2, 3, 4, 5, 6, 7, 8, "nine"]

As you can see, the `concat` method can merge multiple arrays and other types of values ​​into a new array.

In contrast, the `push` method can only be used to add elements to the end of an array and cannot merge other arrays or values.

In addition, it should be noted that the `concat` method and the `push` method both return a new array or a modified array, and do not return a copy of the original array. Therefore, when using these two methods, you need to assign the return value to a new variable to save the merged array, or use a reference to the original array directly.

To summarize, `concat` and `push` are two methods used for array operations in JavaScript. Their differences are mainly reflected in the following aspects:

1. `concat` The method is used to merge two or more arrays into a new array. It does not modify the original array and returns the new array. The `push` method is used to add one or more elements to the end of the array. It modifies the original array and returns the modified one. The new length of the array.

2. The `concat` method can merge any number of arrays and other types of values, while the `push` method can only add elements to the end of the array and cannot merge other arrays or values.

3. The `concat` method returns the new merged array and will not change the original array; the `push` method returns the new length of the modified array and will change the original array.

In actual applications, you can choose to use the `concat` method or the `push` method according to specific needs and scenarios, which can flexibly perform array operations and element additions.

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