Summary of basic knowledge of javascript Array object_javascript skills

My summary of ideas for Array objects is: 5 methods, 3 moves, 12 formulas

1. Declaring the 5th method: only for one-dimensional arrays, of course, there are also two-dimensional and three-dimensional arrays, so I won’t explain it here.

Copy the code The code is as follows:

var a = new Array();
var a = new Array;
var a = new Array(10);//Create an Array object and specify the number of items in the array
var a = new Array("red","blue ","green");
var a = ["red"," blue"," green"];

2. Attribute 3 tricks: constructor, length, prototype
constructor represents a function that creates an object. The constructor property is a member of all objects that have a prototype. They include all JScript native objects except Global and Math objects. The constructor property holds a reference to the function that constructs a specific object instance. For example:

Copy code The code is as follows:

x = new String("Hi");
if (x.constructor == String)
// Process (condition is true).
or
function MyFunc {
// Function body.
}
y = new MyFunc;
if (y.constructor == MyFunc)
// Process (condition is true).

Length represents the length of the array and how many items there are. I won’t write an example here.
prototype returns a reference to the prototype of the object type. Use the prototype property to provide a basic set of functionality for an object's class. New instances of an object "inherit" the operations assigned to the object's prototype.
For example, add a method to an Array object that returns the value of the largest element in the array. To accomplish this, declare the function, add it to Array.prototype, and use it.

Copy code The code is as follows:

function array_max( ){
var i, max = this[0];
for (i = 1; i < this.length; i )
{
if(max < this[i])
max = this[i] ;
}
return max;
}
Array.prototype.max = array_max;
var x = new Array(1, 2, 3, 4, 5, 6);
var y = x.max( );

After this code is executed, y saves the maximum value in the array x, or 6.
3. Method 12: concat method | join method | pop method | push method | reverse method | shift method | unshift method | slice method | splice method | sort method | toString method | valueOf method

Copy code The code is as follows:

//1.concat(): Returns a new array, which is a combination of two or more arrays.
var a1 = [1,2,3,4];
var a2 = a1.concat("5",'6');
alert(a2); //Result: 1,2 ,3,4,5,6
//2.join(): Returns a string value that contains all elements of the arrays connected together, with the elements separated by the specified delimiter.
var a1 = [1,2,3,4];
var a2 = a1.join();
var a3 = a1.join(",");
var a4 = a1 .join("|");
alert(a2); //Result: 1,2,3,4
alert(a3); //Result: 1,2,3,4
alert (a4); //Result: 1|2|3|4
//3.pop(): Remove the last element in the array and return the element. If the array is empty, undefined will be returned.
var a1 = [1,2,3,4];
var item = a1.pop();
alert(item); //Result: 4
alert(a1);/ /Result: 1,2,3
//4.push(): Add (append) new elements to an array and return the new length value of the array. The push method will add new elements in the order they appear. If one of the arguments is an array, the array is added to the array as a single element. If you want to combine elements from two or more arrays, use the concat method.
var a1 = [1,2,3,4];
a1.push(5);
a1.push("6");
alert(a1);//Result: 1,2,3,4,5,6
//5.reverse(): Returns an Array object with the order of elements reversed.
var a1 = [1,2,3,4];
a1.reverse();
alert(a1);//Result: 4,3,2,1
//6 .shift(): Removes the first element in the array and returns that element.
var a1 = [1,2,3,4];
a1.shift();
alert(a1);//Result: 2,3,4
//7.unshift (): Insert the specified element into the beginning of the array and return the array.
var a1 = [1,2,3,4];
a1.unshift(5);
alert(a1);//Result: 5,1,2,3,4
//8.slice(): Returns a segment of an array. a1.slice(start, [end]), the slice method copies up to, but does not include, the element specified by end. If start is negative, treat it as length start, where length is the length of the array. If end is negative, it is treated as length end, where length is the length of the array. If end is omitted, the slice method copies until the end of arrayObj. If end appears before start, no elements are copied to the new array.
var a1 = [1,2,3,4];
var a2 = a1.slice(-1);
var a3 = a1.slice(0,-1);
var a4 = a1.slice(1);
alert(a2);//Result: 4
alert(a3);//Result: 1,2,3
alert(a4);//Result ：2,3,4
//9.splice(): Remove one or more elements from an array, if necessary, insert a new element at the position of the removed element, and return the removed element .
//arrayObj.splice(start, deleteCount, [item1[, item2[, . . . [,itemN]]]])
var a1 = [1,2,3,4];
var a2 = a1.splice(1,0);
var a3 = a1.splice(1,1);
var a4 = a1.splice(1,1,"5");
alert (a2);//Result:
alert(a3);//Result: 2
alert(a1);//Result: 1,5,4
//10.sort(): Return An Array object whose elements have been sorted.
var a1 = [2,3,1,4,"b","a"];
var a2 = a1.sort();
alert(a2);//Result: 1, 2,3,4,a,b
//11.toString(): Returns the string representation of the object.
var a1 = [1,2,3,4,"b","a"];
var a2 = a1.toString();
alert(a2);//Result: 1, 2,3,4,b,a
//12.valueOf(): Returns the original value of the specified object.
var a1 = [1,2,3,4,"b","a"];
var a2 = a1.valueOf();
alert(a2);//Result: 1, 2,3,4,b,a

indexOf extension:

Copy code The code is as follows:

if (!Array.prototype.indexOf) Array.prototype.indexOf = function(item, i) {
i || (i = 0);
var length = this.length;
if (i < 0) i = length i;
for (; i < length; i )
if (this[i] === item ) return i;
return -1;
};
function testIndexOf()
{
var a =[1,2,3,4];
alert(a. indexOf(3));
}

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