The addition and deletion of js array elements have been confusing. Today I finally found the detailed description. I will give me a code to test it first^-^
The code copy 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 the parameter to the beginning of the original array and return 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 in IE6.0 is always undefined, and the test return value in FF2.0 is 7, so the return value of this method is unreliable. When you need to use the return value, you can use splice 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 the parameter 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 composed of 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,...): DeleteCount item from the start position, and insert val1,val2,...
When clearing the array, just pass the startIndex.
If all elements are not deleted, pass the deleteCount parameter.
splice also has the function of deleting first and then adding, that is, delete several elements first, and then add several elements at the deleted position. The number of deleted and added elements must not be equal. At this time, deleteCount is also used.
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 shift
a.splice(0,0,-2,-1); var b = a.length;//Same unshift
var b = a.splice(a.length-1,1);//Same pop
a.splice(a.length,0,6,7); var b = a.length; //Same push
reverse: Inverse the array
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 by 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 a new array composed of items from the specified start subscript to the end subscript in the original array.
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): group the elements of the array into a string, with separator as the separator. If omitted, use commas as the separator by default.
var a = [1,2,3,4,5];
var b = a.join("|"); //a: [1,2,3,4,5] b: "1|2|3|4|5"
Here is another way to use array 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 array that appends into a string
};
}
Today, I suddenly discovered that join is a good way to convert arrays into strings in the application, so I encapsulated them into objects and used:
/**
*Convert arrays into strings that are split by specific symbols
*/
function arrayToString(arr,separator) {
if(!separator) separator = "";// If separator is null, it will be empty by default
return arr.join(separator);
}
/**
* Find the string contained in the array
*/
function arrayFindString(arr,string) {
var str = arr.join("");
return str.indexOf(string);
}