ES6---Extension operators and rest ' ... ' (three-point operators), in arrays, functions, SET/MAP, etc.

ES6 's new three-point operator, which is represented by three dots, plays an important role in the array, can be combined and decomposed into arrays, can transform data structures such as set, and can simplify the representation of function parameters, and then we uncover the mystery ...

Three-point-rest parameter:

Let fun1=function(... args) {For (let Arg of args) {console.log (arg);}; Console.log (args)};fun1 (' A ',' B ',' C ');A b c,[a,b,c]fun1 (1,2);1 2,[1,2] ... args represents all the parameters, regardless of the number of arguments passed through args can be traversed, and args sets all the parameters of the parameter array let fun2=function(Arr,. args) {console.log (arr); Console.log (args);}; Fun2 (1,2,3);  1, [2,3]fun2 (1); function (arr1,.. ARGS,ARR2) {console.log (args);} //at this time error!!! Remember, three is a rest parameter, and no more arguments can be followed, only as the last character! //////////////////////////[x,... y]=[1, 2,3];console.log (y); //[2,3][x,... y,z]=[1,2,3]; //error, Rest element must is last element in array       

As a rest parameter, the three-point operator can play an important role in functions, deconstruction assignments, and so on. ' As the name ', rest means the rest, it pushes the remaining number of arguments into the array, so it inherits the method of the array. The rest parameter can only appear in the last one, or it will be an error, of course, to expand the identity of the operation is a matter of case.

Three o'clock-extended operator:

Let arr=[1,2,3];console.log (... arr.);1, 2, 3 returns the items in the arrayLet a=[2,3];console.log (1,... A,4);The 1,2,3,4 extension operator can be placed in the middleLet Divs=document.queryselectorall (' Div '); [... divs];Array[300],[] DIVs can be transformed into an array, Console.log (... divs);Div1,div2 .... Traversing divs ItemsLetset=New Set ([1,2,3,3]); [...Set];Returns an array of [all-in-a-Let map= new Map ([[1, ' a '],[2, ' B '],[3, ' C ']); [... Map.keys]; //returns [All-in-all], an array of attributes; [... map.values]; //return [a,b,c],value array //////////// ///[...  ' Wbiokr ']; //["W", "B", "I", "O", "K", "R"] traverse strings, return each character; let Str= ' abc '; [ ' aaa ',... str, ' CCC ']; //[aaa, A, B, C, CCC] extended operator location more capricious         

A three-point extension operator that expands an array or class array object into a series of comma-separated sequence of values, which is like the inverse of a rest parameter.

ES6---Extension operators and rest ' ... ' (three-point operators), in arrays, functions, SET/MAP, etc.