JS Generator Data type

1. Overview

Generator is a new data type introduced by ES6 and looks like a function that yields can be returned multiple times, in addition to returning with return.

Generator is defined by the function*, (note the * number),

2. Example

Functions cannot save state, sometimes global variables are required to hold numbers;

2.1

' Use strict ';functionnext_id () {varID = 1;  while(id<100) {yield id; ID++; }   returnID;}//Test:varx, pass=true, G=next_id (); for(x = 1; x < x + +)) {    if(G.next (). Value!==x) {Pass=false; Alert (' Test failed! ');  Break; }

}if(pass) {alert (' Test pass! ');}

2.2 An iterative iterator with infinite loops

function* idmaker () {    var index = 0;      while (true)        yield index+ +;} var // "Generator {}"  /  /0//  1//  2

2.3generator.prototype.next ()

When the iteration ends, Generator.next (). Done ===true, before end ===false

function* gen () {   1;   2;   3;} var // "Generator {}"g.next ();      // "Object {value:1, done:false}"G.next ();      // "Object {value:2, done:false}"G.next ();      // "Object {value:3, done:false}"G.next ();      // "Object {value:undefined, done:true}"

2.4 Generator.prototype.return ();

The return method returns the given parameter value and ends the iterator

Example

function* gen () {   1;   2;   3;} var g = Gen (); G.next ();         // {value:1, done:false}G.return//  {value: "foo", Done:true}g.next (); 
   //  {value:undefined, done:true}

Note If the done value is true, then call return, and the returned value is also undefined

function* Gen () {yield 1;} var g = Gen (); Console.log (G.next ()); // {value:1, done:false}Console.log (G.next ()); // {value:undefined, done:true}Console.log (g.return//{value:undefined, done:true}
    

2.5 Generator.prototype.throw ()

The Thorw () method, by throwing an exception into the iterator, to regain the execution of the iterator;

Returns an object with value and done two properties

function*Gen () { while(true) {    Try{yield42; } Catch(e) {Console.log ("Error caught!"); }  }}varg =Gen ();varA =G.next ();//{value:42, done:false}varb = g.Throw(NewError ("Something went wrong"));//"Error caught!"//{value:42, done:false}Console.log (a); Console.log (B.value+ "::" +b.done);

JS Generator Data type