js操作数组的多种方法 shift()、unshift()、push()、pop()、concat()、slice()、splice()、toString()、join()_array.splice() shif

1.shift() ：把数组的第一个元素从其中删除，并返回第一个元素的值。该方法会改变原数组。

const array=['one','two','three','four'];
const shiftResult=array.shift();
console.log(shiftResult); //one
console.log(array);  // ['two','three','four']

 

2.unshift()：向数组的开头添加一个或更多元素，并返回新数组的长度。该方法会改变原数组。

const array=['one','two','three','four'];
const unshiftResult = array.unshift('new1','new2');
console.log(unshiftResult);//6
console.log(array); //['new1','new2','one','two','three','four']

 

3.push()：向数组的末尾添加一个或多个元素，并返回新的长度。该方法会改变原数组。

const array=['one','two','three','four'];
const pushResult = array.push('new1','new2');
console.log(pushResult);// 6
console.log(array); //['one','two','three','four','new1','new2']

4.pop()：把数组的最后一个元素从其中删除，并返回最后一个元素的值。该方法会改变原数组。

const array=['one','two','three','four'];
const popResult = array.pop();
console.log(popResult);// four
console.log(array);// ['one','two','three']

5.concat()：用于连接两个或多个数组。该方法不会改变现有的数组，而仅仅会返回被连接数组的一个副本。

const array=['one','two','three','four'];
const arrar1=['new3','new4'];
const arrar2 = ['new5', 'new6'];
const concatResult1 = array.concat('new1','new2');
const concatResult2 = array.concat(arrar1);
const concatResult3 = array.concat(arrar1, arrar2);
console.log(concatResult1);//['one','two','three','four','new1','new2']
console.log(concatResult2);//['one','two','three','four','new3','new4']
console.log(concatResult3);//['one','two','three','four','new1','new2','new3','new4']
console.log(array);//['one','two','three','four']

6.slice(start，end):截取数组的某一部分，该方法并不会修改数组，而是返回一个子数组，包含从 start 到 end （不包括该元素）的 arrayObject 中的元素。
 

const array=['one','two','three','four','five','six','seven'];
const sliceResult1 = array.slice(-4,-2);
const sliceResult2 = array.slice(-2);
const sliceResult3 = array.slice(2,6);
const sliceResult4 = array.slice(2);
console.log(sliceResult1); //['four','five'];
console.log(sliceResult2);//['six','seven'];
console.log(sliceResult3);//['three','four','five','six'];
console.log(sliceResult4);//['three','four','five','six','seven'];
console.log(array);//['one','two','three','four','five','six','seven'];

7.splice(index,howmany,item1, ..., itemX)： 向/从数组中添加/删除项目，然后返回被删除的数组。该方法会改变原始数组。

//向原数组某个位置添加一个元素
const array=['one','two','three','four'];
array.splice(2,0,'new1');
console.log('array:', array);//['one','two','three','new1','four']

//删除位于 index 2 的元素，并添加一个新元素来替代被删除的元素
 const array=['one','two','three','four'];
 array.splice(2,1,'new1');
 console.log('array:', array);//['one','two',new1','four']

//删除从 index 2  开始的三个元素，并添加一个新元素来替代被删除的元素
 const array=['one','two','three','four','five','six','seven'];
 array.splice(2,3,'new1');
 console.log('array:', array);//['one','two','new1','six','seven']

8.toString():可把一个逻辑值转换为字符串，并返回结果。

const array=['one','two','three','four'];
const toStringResult = array.toString();
console.log('array:', toStringResult);//'one,two,three,four'

9.join(separator)：把数组中的所有元素放入一个字符串。

const array=['one','two','three','four'];
const joinResult = array.join();
const joinResult1 = array.join('/');
console.log(joinResult);//"one,two,three,four"
console.log(joinResult1);//"one/two/three/four"