Which arrays can be merged in javascript

JavaScript is a popular programming language commonly used for web development and web page interaction. In JavaScript, arrays are a very important data type that are often used to store and process multiple values. When using arrays, we often encounter situations where two or more arrays need to be merged. So, in JavaScript, which arrays can be merged? This article will introduce array merging methods in JavaScript and analyze their advantages and disadvantages.

1. concat() method

The concat() method in JavaScript is a method used to connect two or more arrays. It does not modify the original array, but returns a new array containing the elements of all concatenated arrays. The specific usage is as follows:

var array1 = [1, 2, 3];
var array2 = [4, 5, 6];
var array3 = array1.concat(array2);
console.log(array3);   // [1, 2, 3, 4, 5, 6]

As can be seen from the above code, the concat() method will start from array array1, add all elements to the new array, and then add all elements in array array2 to the new array. in the array. It will return a new array containing all elements of array1 and array2.

Advantages:

1. Can merge multiple arrays;
2. The original array will not be modified;
3. The syntax is simple and easy to understand.

Disadvantages:

1. If multiple arrays need to be merged, a large number of intermediate arrays will be generated, affecting performance;
2. If the original array is large, then The new array generated is also large and may cause memory issues.

2. Push() method and loop

Another way to merge arrays is to use the push() method and a loop. The specific method is to add the elements of one array to another array one by one. The specific usage method is as follows:

var array1 = [1, 2, 3];
var array2 = [4, 5, 6];
for(var i=0; i<array2.length;i++){
  array1.push(array2[i]);
}
console.log(array1);   // [1, 2, 3, 4, 5, 6]

As can be seen from the above code, this method first defines two arrays array1 and array2, and then uses a for loop to traverse all the elements in array array2 and add them to array array1 one by one. middle.

Advantages:

1. Can merge multiple arrays;
2. Can avoid generating a large number of intermediate arrays.

Disadvantages:

1. Each array needs to be looped and traversed multiple times, resulting in poor performance;
2. If you want to merge multiple arrays, This method needs to be used multiple times, and the code complexity is high.

3. Spread operator

The spread operator (spread operator) in ES6 is a very powerful syntax that can expand an array into a sequence. The specific usage method is as follows:

var array1 = [1, 2, 3];
var array2 = [4, 5, 6];
var array3 = [...array1, ...array2];
console.log(array3);   // [1, 2, 3, 4, 5, 6]

As can be seen from the above code, the expansion operator can expand array array1 into a sequence, and then expand array array2 into a sequence, and then connect the two sequences together. Generate a new array array3.

Advantages:

1. The syntax is simple and easy to understand;
2. The code is concise and clear.

Disadvantages:

1. is not suitable for operating large arrays and may cause memory problems.

4. Summary

In JavaScript, many methods can be used to merge arrays, including concat() method, push() method, loop and spread operator. They each have advantages and disadvantages and are suitable for different scenarios. If you need to merge multiple arrays and the original array is small, you can use the concat() method. If you need to merge multiple arrays and the original array is relatively large, you should avoid using the concat() method and instead use the push() method and a loop, or use the spread operator. In actual development, appropriate methods should be selected according to different needs to improve code efficiency and performance.

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