How to fill an array with fixed elements in js

In the previous article, we learned about whether elements can pass the test of the specified function. Please see "Can the elements pass the test of the specified function when using js arrays". This time we will learn how to fill an array with fixed values. You can refer to it if you need it.

Before we knew how to convert array elements into strings, how to test whether the elements can pass the specified function, and what the length of the array is. Today we will introduce how to fill the array with fixed elements. What is the method.

First let’s look at a small example.

<script>
var arr = new Array(7); 
arr[0] = "one";
arr[1] = "two";
arr[2] = "three";
console.log(arr.fill("four",3,6));
</script>

The result of this small example is

We can see that the previous results are very normal, among which the third and fourth Fifth, these three elements are all "four", but the last one is empty. Let's take a look at the code again. The fill method we use, our parameter naming selection is "3-6", so why is the last one not filled in?

Let’s take a closer look at this method.

fill() method fills all elements in an array from the starting index to the ending index with a fixed value. Excludes terminating index.

Let’s take a look at the syntax of this method.

arr.fill(用来填充数组元素的值,起始索引,终止索引)

The fill method accepts three parameters, the last two are optional. Their default values ​​are 0 and the value of this object's length attribute. If the start index is negative, the start index is automatically calculated as "array_length_start_index", where array_length is the value of this object's length attribute. If the end index is negative, the end index is automatically calculated as "array length end index".

The fill method is deliberately designed as a general method, which does not require it to be an array object. This method is a mutable method that changes the this object on which it is called and returns it, rather than returning a copy. When an object is passed to the fill method, the array will be filled with a reference to the object.

That’s all. If you need it, you can read: javascript advanced tutorial

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