[js] basic syntax - for loop

Array , Map and Set The cycle of ： for of / forEach
The loop of objects ： for in

1. Array of for loop – for (… of … ) / forEach / for (var i=0; i< length ; i++)

   var a = [1,2,3,4,5];
   for (var each of a){
         
   	console.log(each);
   }
   

   var a = [1,2,3,4,5];
   a.forEach(function (element){
         
   	console.log(element);
   })
   

   var a = [1,2,3,4,5];
   for (var i=0; i<a.length; i++){
         
   	console.log(a[i]);
   }
   

   

2. Object's for loop – for (… in …) {…}

   var obj1 = {
         'a':1, 'b':2, 'c':3};
   for (var key in obj1){
         
   	console.log(key, obj1[key]);
   }
   

   

3. Map and Set Of for loop – for ( … of …) / forEach()

   var m = new Map([['a', 1], ['b',2], ['c', 3]])
   for (var element of m){
         
   	console.log(element[0], element[1]);
   }
   

   

   var m = new Map([['a', 1], ['b',2], ['c', 3]])
   m.forEach(function (value, key, map){
         
   	console.log(key, value);
   })
   

   

   var s = new Set([1,2,3,4,5]);
   s.forEach(function (element){
         
   	console.log(element);
   })