Summary of methods to loop through Array and Map in JavaScript

js loops through array methods
eg1:

for (var i = 0; i < myStringArray.length; i++) { 
 alert(myStringArray[i]); 
 //Do something 
} 

eg2:

Array.prototype.foo = "foo!"; 
var array = ['a', 'b', 'c']; 
 
for (var i in array) { 
 alert(array[i]); 
} 
 
for(var i in this.$GLOBAL_DETAIL.album_photo_ids){if(this.$GLOBAL_DETAIL.album_photo_ids[i] == "3487675024077108") alert(this.$GLOBAL_DETAIL.album_photo_ids[i]);} 

eg3:

[1,2,3,4].map( function(item) { 
   alert(item); 
}) 

eg4:

var x = [1,2,3,4].map( function(item) { return item * 10; } ); 
 
// And now x is [10,20,30,40] 

eg5:

var myStringArray = [ "Hello", "World" ] 
var len = myStringArray.length 
for (var i=0; i<len; ++i) { 
 if (i in myStringArray) { 
 var s = myStringArray[i]; 
 ... do something with s ... 
 } 
} 

eg6:

var myStringArray = [ "Hello", "World" ] 
myStringArray.forEach( function(s) { 
  ... do something with s ... 
} ) 

eg7:

var i=0,item,items = ['one','two','three']; 
while(item=items[i++]){ 
 console.log(item); 
} 
 
// logs: 'one','two','three' 
 
and for the reverse order, an even more efficient loop 
var items = ['one','two','three'], i=items.length; 
while(i--){ 
 console.log(items[i]); 
} 
 
// logs: 'three','two','one' 
 
or the classical for loop 
var items = ['one','two','three'] 
for(var i=0,l=items.length; i < l ; i++){ 
 console.log(items[i]); 
} 
 
// logs: 'one','two','three' 

eg8:

var myStringArray = ['Hello', 'World']; // array uses [] not {} 
for (var i in myStringArray) { 
 console.log(i + ' -> ' + myStringArray[i]); // i is the index/key, not the item 
} 

js loop through map to get all key and value
eg1:

//Page address  
 pageUrl : { 
  menu   : "loadPage.htm?url=/collect/menu.page",   //  Enter the menu page  
  guangfaPage  : "loadPage.htm?url=/collect/menu.page",   //  Enter the information collection page of Guangfa  
  pinganPage  : "loadPage.htm?url=/collect/menu.page",   //  Enter the safe information collection page  
  nuonuoPage  : "loadPage.htm?url=/collect/menu.page",   //  Enter the information collection page of Nono  
  youbangPage  : "loadPage.htm?url=/collect/menu.page",   //  Enter AIA information collection page  
  inputMobileNo : "loadPage.htm?url=/collect/inputMobileNo.page", //  Enter the input mobile phone number page  
  readIdCard  : "loadPage.htm?url=/collect/readIdCard.page",  //  Enter the read ID page  
  member   : "loadPage.htm?url=/collect/member.page",   //  Enter the input member card number page  
  bankCard  : "loadPage.htm?url=/collect/bankCard.page",   //  Enter the insert bank card page  
  url   : "loadPage.htm?url=/collect/url.page"    //  Enter the jump url page  
 }, 
 
for(var key in this.pageUrl){ 
 alert(key+" : "+this.pageUrl[key]); 
} 

eg2:

var obj = { 
 "a": 1, 
 "b": 2, 
 "c": 3 
}; 
 
for (var prop in obj) { 
 if (obj.hasOwnProperty(prop)) { 
 // or if (Object.prototype.hasOwnProperty.call(obj,prop)) for safety... 
 alert("prop: " + prop + " value: " + obj[prop]) 
 } 
} 

Double Map loop
eg:

Array.prototype.foo = "foo!"; 
var array = ['a', 'b', 'c']; 
 
for (var i in array) { 
 alert(array[i]); 
} 
 
for(var i in this.$GLOBAL_DETAIL.album_photo_ids){if(this.$GLOBAL_DETAIL.album_photo_ids[i] == "3487675024077108") alert(this.$GLOBAL_DETAIL.album_photo_ids[i]);} 

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