Common ways to manipulate arrays

Map () Map

function map(){    var arr = [1,2,3,4,5];    arr.map(function(val,index){        console.log(val * 2);    })}//map();      //2 4 6 8 10

Filter () Filtering

function filter(){    var arr = [1,2,3,4,5,6,7];    var arr1 = arr.filter(function(val,index){        return val < 4 ;    })    console.log( arr1 );   //[1,2,3]    var arr2 = arr.filter(function(val,index){  //定义一个变量名接一下        return index < 3;    })    console.log( arr2 );    //[1,2,3]}//filter();

Known an array [' A ', ' B ', ' C ', ' d ', ' e ', ' f '], using at least three methods, remove the third-digit element from the array, and get a new array of [' A ', ' B ', ' C ']. */

//var arr = [‘a‘,‘b‘,‘c‘,‘d‘,‘e‘,‘f‘]//var arr1 = arr.filter(function(val,index){    //return index < 3;//})//console.log(arr1)

Push () adds one or more elements to the end of the array and returns the new length

function push(){    var arr = [1,2,3];    arr.push(2,3,4);    console.log(arr);}//push();    //[1,2,3,2,3,4]function push2(){    var arr1 = [1,2,3];    var arr2 = [4,5,6];    arr1.push( arr2 );    return arr1;}console.log( push2() )   //[ 1,2,3,[4,5,6] ]

Unshift () adds one or more elements to the beginning of the array and returns the new length

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

Pop () deletes the last element of the array and returns the value of the deleted element

function pop(){    var arr = [1,2,3];    arr.pop();    console.log(arr);  //[1,2]}//pop();

Shift () deletes the first value of the array and returns the value of the deleted element

function shift(){    var arr = [1,23,4];    arr.shift();    console.log(arr);  //[23,4]}//shift();

The concat (3,4) method is used to connect two or more arrays

function concat(){    var arr1 = [1,2,3];    var arr2 = [4,5,6];    console.log( arr1.concat(arr2) )   //[1, 2, 3, 4, 5, 6]    console.log( arr1.concat(1,2,3))   //[1, 2, 3, 1, 2, 3]}//concat();

Reverse () reverse the array

function reverse(){    var arr = [1,2,3,4,5,6,7,8];    console.log( arr.reverse() )   //[8, 7, 6, 5, 4, 3, 2, 1]}//reverse();

The---Splice () method is different from the slice () method, and the splice () method modifies the group directly slice (start,end) returns a new array that consists of the entries from the original array that specify the starting subscript to the end subscript

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

The splice () method adds/deletes an item to/from the array and then returns the item that was deleted

function splice(){    var arr = [1,2,3,4,5,6,7];    console.log( arr.splice(0,3) );  //[1,2,3]}//splice();

Join (separator) sets the element group of the array to a string, separator as a delimiter, and the default with a comma delimiter if omitted

function join(){    var arr = [1,2,3,4,5,6,7];    return arr.join("|");}//console.log( join() )     //"1|2|3|4|5|6|7"function join2(){    var arr = [1,2,3,4,5];    arr.join();    return arr.join().slice(0,3);}//console.log( join2() )  //1,2

Common ways to manipulate arrays