JavaScript simulation push_javascript trick

Task: First I defined a variable var arr = [0,1,2,3,4,5]; I now want to simulate the push method to add something after 5 in this array, we What should be done? I'll give you 5 minutes to think. Please don't look down before you think about it.

Analysis: We want to add something to the end of this array, right? The key point is how we can find the last position of the element. Let's not consider the last position first. Let's first think about how we usually access the contents of an array. Is it like this arr[n], right? If we access an index larger than this array, it will be undefined. To put it simply, if there is no such index, it will be undefined. If we keep adding 1 to the index of this array, then if undefined appears, is it the position we are looking for? Although this method is OK, I have a better way to use The length attribute can get the length of this array. Then this length is the index of this array + 1. We just want to add content to this index.

Code:

var arr = [0,1,2,3,4,5];
arr.length 获取这个数组的最后位置

Task: Now that we have obtained the last position of the array, we can add content to it. So how to add it? To whom to add and how to add.

Analysis: Now think about the ways to add content to an array? The length obtained is the position we want to add.

Synthesis:

var arr = [0,1,2,3,4,5];
function Push(value){
arr[arr.length] = value;
}
Push(6);
console.log(arr); //[0, 1, 2, 3, 4, 5, 6]

Task: Although you can now add content to it, you can only add one at a time. What should I do?

Analysis: I miss my old friend for suddenly. This old friend can help us complete some repetitive things, so let’s ask him to help us.

Code:

Analysis: How should we write this for? How much smaller is i? Is it just as many as we add? So how many bits do we need to add? It seems that we really don’t know, but an old friend knows that he is arguments, which can get the parameters we pass in, and it is a pseudo-array, which means that it can also use the length attribute like an array to get the parameters we pass in. The actual parameter length.

Code:

for(var i=0;i<arguments.length;i++){}

Analysis: So now the question is, what content do we add to where? Going back to our task, do we want to add the content we passed in to the last position of an array? , so how to get the content we passed in? We seem to have said that arguments can get its content.

Code:

var arr = [0,1,2,3,4,5];
function Push{
for(var i=0;i<arguments.length;i++){
arr[arr.length] = arguments[i];
}
}
Push(6,7,8);

Done.

Extracurricular expansion: friends with basic knowledge
Ok, although the task has been completed, the problem now is that this code can only serve the array arr. If we want to provide this function for all arrays, we need to add this method to the prototype of Array.

var arr = [0,1,2,3,4,5];

Array.prototype.Push = function{
for(var i=0;i<arguments.length;i++){
this[this.length] = arguments[i];
}
}
arr.Push(1,2,3)

Change the arr inside to this. This means whoever calls it. If you want to know more about this, you can read to fully understand the pointing of this in js. You don’t have to memorize this article.