Summary of array appending methods in javascript_javascript skills

Adding elements to an array in JavaScript is a very simple problem. JavaScript itself provides a large number of such functions. We can use js’s own functions to quickly add elements to an array. This article explains how to append an array in JavaScript. Summary below.

In the past, the method arr.concat(arr2) was commonly used to append arrays. The example is as follows:

Copy code The code is as follows:

Many people have been confused about the addition and deletion of js array elements. Here is the following test code:

Copy code The code is as follows:

var arr = new Array();
arr[0] = "aaa";
arr[1] = "bbb";
arr[2] = "ccc";
//alert(arr.length);//3
arr.pop();
//alert(arr.length);//2
//alert(arr[arr. length-1]);//bbb
arr.pop();
//alert(arr[arr.length-1]);//aaa
//alert(arr.length); //1
var arr2 = new Array();
//alert(arr2.length);//0
arr2[0] = "aaa";
arr2[1] = " bbb";
//alert(arr2.length);//2
arr2.pop();
//alert(arr2.length);//1
arr2 = arr2.slice (0,arr2.length-1);
//alert(arr2.length);//0
arr2[0] = "aaa";
arr2[1] = "bbb";
arr2[2] = "ccc";
arr2 = arr2.slice(0,1);
alert(arr2.length);//1
alert(arr2[0]);/ /aaa
alert(arr2[1]);//undefined
shift: delete the first item of the original array and return the value of the deleted element; if the array is empty, return undefined
var a = [1 ,2,3,4,5];
var b = a.shift(); //a: [2,3,4,5] b: 1
unshift: Add parameters to the beginning of the original array , and returns the length of the array
var a = [1,2,3,4,5];
var b = a.unshift(-2,-1); //a: [-2,- 1,1,2,3,4,5] b: 7
Note: The test return value under IE6.0 is always undefined, and the test return value under FF2.0 is 7, so the return value of this method is unreliable , when you need to use the return value, splice can be used instead of this method.
pop: delete the last item of the original array and return the value of the deleted element; if the array is empty, return undefined
var a = [1,2,3,4,5];
var b = a.pop(); //a：[1,2,3,4] b：5 //If you don’t need to return, just call it directly
push: Add parameters to the end of the original array and return the length of the array
var a = [1,2,3,4,5];
var b = a.push(6,7); //a: [1,2,3,4,5,6, 7] b: 7
concat: Returns a new array, which is formed by adding parameters to the original array
var a = [1,2,3,4,5];
var b = a .concat(6,7); //a：[1,2,3,4,5] b：[1,2,3,4,5,6,7]
splice(start,deleteCount,val1 ,val2,...): Delete the deleteCount item from the start position and insert val1, val2,...
var a = [1,2,3,4,5];
var b = a.splice(2,2,7,8,9); //a：[1,2,7,8,9,5] b：[3,4]
var b = a. splice(0,1); //Same as shift
a.splice(0,0,-2,-1); var b = a.length; //Same as unshift
var b = a.splice( a.length-1,1); //Same as pop
a.splice(a.length,0,6,7); var b = a.length; //Same as push
reverse: reverse the array Order
var a = [1,2,3,4,5];
var b = a.reverse(); //a：[5,4,3,2,1] b：[5 ,4,3,2,1]
sort(orderfunction): Sort the array according to the specified parameters
var a = [1,2,3,4,5];
var b = a .sort(); //a: [1,2,3,4,5] b: [1,2,3,4,5]
slice(start,end): Returns the specified start from the original array A new array composed of items between the subscript and the end subscript
var a = [1,2,3,4,5];
var b = a.slice(2,5); //a :[1,2,3,4,5] b:[3,4,5]
join(separator): Combine the elements of the array into a string, with separator as the separator. If omitted, the default will be used Use commas as separators
var a = [1,2,3,4,5];
var b = a.join("|"); //a: [1,2,3,4 ,5] b: "1|2|3|4|5"
Give me another method of using arrays to simulate javaStringBuffer to process strings:
/**
* String processing function
*/
function StringBuffer()
{
var arr = new Array;
this.append = function(str)
{
arr[arr.length] = str;
};
this. toString = function()
{
return arr.join(""); //Ping the appended array into a string
};
}
Suddenly in the application today I found that join is a good way to convert an array into a string, so I encapsulated it into an object and used:
/**
* Convert the array into a string separated by specific symbols
*/
function arrayToString(arr,separator)
{
if(!separator) separator = "";//If separator is null, it defaults to empty
return arr.join(separator);
}
/**
* Find the string contained in the array
*/
function arrayFindString (arr,string)
{
var str = arr.join("");
return str.indexOf(string);
}

Finally, there are some problems encountered when push.apply appends to an array. A test for friends who like to play with a.push.apply(a, b);
a.push.apply(a, b); This is a way of writing that I think is cool and does not require a for loop. I have never encountered any problems. It was not until today that the b I wanted to append was a very large array and I encountered a pitfall.

Copy code The code is as follows:

a = new Array(); >b = new Array(125624);                                                            

The above code throws the following exception under chrome on mac

Uncaught RangeError: Maximum call stack size exceeded

If you change the array to b = new Array(125623); a smaller element will be fine. After testing, other browsers also have large arrays. Error problem, but different browsers have different critical values ​​

The suggestion given here is to use forEach honestly, which can not only avoid the abnormal problem of large arrays, but also consider forEach from a performance perspective. The fastest