1:js Medium splice Method

　　splice(index,len,[item])    notes ： This method changes the original array .

splice Yes 3 Parameters , It can also be used to Replace / Delete / add to One or more values in the array

index: Array start subscript         len: Replace / Deleted length        item: Replacement value , If the operation is deleted item It's empty

Such as ：arr = ['a','b','c','d']

Delete ----  item Not set up

arr.splice(1,1)   //['a','c','d']          Delete the starting subscript as 1, The length is 1 A value of ,len Set up 1, If 0, Then the array remains the same

arr.splice(1,2)  //['a','d']          Delete the starting subscript as 1, The length is 2 A value of ,len Set up 2

Replace ---- item Replace with a new value

arr.splice(1,1,'ttt')        //['a','ttt','c','d']         Replace starting subscript is 1, The length is 1 One of the values of is ‘ttt’,len Set up 1

arr.splice(1,2,'ttt')        //['a','ttt','d']         Replace starting subscript is 1, The length is 2 The two values of are ‘ttt’,len Set up 1

 

add to ----  len Set to 0,item For added value

arr.splice(1,0,'ttt')        //['a','ttt','b','c','d']         It means that the subscript is 1 Add an item at ‘ttt’

It seems that splice The most convenient

2：delete       delete After deleting the elements in the array , The subscript value will be set to undefined, The length of the array does not change

Such as ：delete arr[1]  //['a', ,'c','d']      Two commas appear in the middle , The length of the array remains the same , One is undefined