What are the methods of array objects in Es5 and what are the new methods in ES6

stay ES5 Common methods of array objects in ：

1、concat() Connect two or more arrays , And return the result

<script>
            let arr=[1,2,3]
			let arr1=[4,5,6]
			var re = arr.concat(arr1);
			console.log(re);//[1,2,3,4,5,6]
</script>

2、join() Put all the elements of the array into a string , The element is divided by the specified separator

<script>
            let arr=[1,2,3]
			var re = arr.join("*")
			console.log(re); //1*2*3
</script>

3、pop() Delete and return the last element of the array , Similarly shift() Delete and return the first element of the array

<script>
            let arr=[1,2,3]
			var re = arr.pop()
            console.log(re)//3
            re1 = arr.shift()
			console.log(re1); //1
</script>

4、 push Add one or more elements... To the end of the array , And return the length of the new array , Similarly unshift() Add one or more elements to the header of the array , And returns the new length

<script>
            let arr=[1,2,3]
			var re = arr.push(4)
            console.log(re)//4
            re1 = arr.unshift(0)
			console.log(re1); //5
            console.log(arr) // [0,1,2,3,4]
</script>

 5、reverse() Reverse the order of the elements in the array

<script>
            let arr=[1,2,3]
			var arr1=arr.reverse()
co          console.log(arr1)//[3,2,1]
</script>

 6、sort() Sort elements of an array

<script>
            let arr=[1,8,3,42,3]
			var arr1=arr.sort()
             console.log(arr1)//[1,3,3,8,42]
</script>

7、 splice() Delete several elements in the specified position , Then add new elements ; It can be seen as pop、push、shift、unshift The synthesis of these methods .

<script>
             // As pop() when , Do not write the added number , Just delete 
            var arr=[10,30,40,5,6]
            var re=arr.splice(4,1)// From the subscript 4 To delete 1 Elements 
			console.log(re,arr) //[6] [10,30,40,5]
            // As push when , Don't delete , Just add 
            var arr=[10,30,40,5,6]
            var re=arr.splice(4,0,7)// From the subscript 4 To delete 0 Elements , add to 7
            console.log(re,arr) //[] [10,30,40,5,6,7]
            //shift() unshift() similar 
            // comprehensive 
            var arr=[10,30,40,5,6]
			var re=arr.splice(2,2,"hello","h5")
            // From the subscript 2 To delete 2 Elements   And insert here "hello","h5"
			console.log(re,arr)//[40,5] [10,30,"hello","h5",6]

</script>

8、slice() Returns the selected element from an existing array , There are two parameters , The first parameter is the starting subscript of the selection , The second parameter is the selected termination subscript , Terminated subscripts cannot be taken , Parameters can take negative numbers , among -1 The subscript of the last number .

<script>
            
            var arr=[10,30,40,5,6]
            var re=arr.slice(0,3)
			console.log(re) //[10,30,40]
             var re1=arr.slice(-3,-1)
            console.log(re1) //[40,5]
</script>

 9、toString() Convert an array to a string , And return the result .

<script>
            let arr=[1,2,3,5,6]
			var re = arr.toString()
			console.log(re);//1,2,3,5,6
</script>

10、toLocaleString() Convert an array to a local string , And return the result , And toString() Basically the same , But notice two differences ：1、 The number format is converted to the thousand separator 2、 Date format conversion

Specify ：

<script>
            let arr=[1,2,3,5,6]
			var re = arr.toLocaleString()
			console.log(re);//1,2,3,5,6

            // difference 1：
            let s=1111
            s.toLocaleString();  // 1,111
            s.toString();  // 1111

            // difference 2：
            const date = new Date();
            date.toString(); // Mon Jul 11 2022 21:27:34 GMT+0800 ( China standard time )
            date.toLocaleString(); // 2022/7/11 21:28:08
</script>

11、valueof() Returns the original value of the array object

<script>
    var  arr=[10,80,30,20]
	console.log(arr.valueOf()) //[10,80,30,20]
</script>

 ES6 New methods for array objects in ：

1、find()： Find the elements in the array that match the criteria , If there are more than one element that meets the criteria , Then return the first element .

<script>
    let arr = Array.of(1, 2, 3, 4);
    console.log(arr.find(item => item > 2)); // 3
    // Writing method of ordinary function 
     console.log(arr.find(function(el){
			if(el>2){
				return true
			}
	})); //3
</script>

 2、findIndex()： Find the index of the eligible elements in the array , If there are more than one element that meets the criteria , Returns the first element index , And find The method is similar .

3、fill()： Fills the contents of array elements with a range of indexes into a single specified value .

<script>
     let arr = Array.of(1, 2, 3, 4);
    //  Parameters 1： The value to fill 
    //  Parameters 2： The starting index to be filled 
    //  Parameters 3( Optional )： Filled end index , The default is the end of the array 
    console.log(arr.fill(0,1,2)); // [1, 0, 3, 4]
</script>

4 、 entrys()： Traversal key value pairs （ The index and elements of the array are traversed as a group ）、keys()： Traversal keys 、values()： Traverse the key values （ understand ）

5、includes()： Whether the array contains the specified value . Be careful ： And Set and Map Of has Method of differentiation ;Set Of has Method is used to find the value ;Map Of has Method is used to find the key name .

<script>
           var arr=[1,,22,3,4,5,,6]
			var re=arr.includes(2)
			console.log(re); //false
</script>

6、flat() Used to reduce the dimension of an array , The parameters in parentheses specify the number of nesting levels of the transformation , Default not to write down one dimension .

<script>
         console.log([1 ,[2, 3]].flat()); // [1, 2, 3]
         console.log([1 ,[2, 3,[22,33,[44,55]]]].flat(2)); // [1, 2, 3,22,33,[44,55]]
</script>

  simulation flat Method , Realization flat The function of ：

<script>
         var arr=[[10,20,30],40,50,[[60,70],80,[90,[110],100]]]
			Array.prototype.myflat=function(num=1){
				var arr=[]
				for(var i=0;i<this.length;i++){
					if(this[i].constructor==Array&&num>0){
						var arr1=this[i].myflat(num-1)
						for(var j=0;j<arr1.length;j++){
							arr.push(arr1[j])
						}												
					}else{
						arr.push(this[i])
					}				
				}
				return arr
			}
			var re2=arr.myflat(1)
			console.log(re2) //[10, 20, 30, 40, 50,[60,70], 80,[90,[110],100]]
</script>