Summary of methods for looping through Array and Map in JavaScript_Basic knowledge

Various methods of looping arrays in js
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 map to get all keys and values
eg1：

//Page地址 
 pageUrl : { 
  menu   : "loadPage.htm?url=/collect/menu.page",   // 进入菜单页面 
  guangfaPage  : "loadPage.htm?url=/collect/menu.page",   // 进入广发信息收集页面 
  pinganPage  : "loadPage.htm?url=/collect/menu.page",   // 进入平安信息收集页面 
  nuonuoPage  : "loadPage.htm?url=/collect/menu.page",   // 进入诺诺信息收集页面 
  youbangPage  : "loadPage.htm?url=/collect/menu.page",   // 进入友邦信息收集页面 
  inputMobileNo : "loadPage.htm?url=/collect/inputMobileNo.page", // 进入输入手机号页面 
  readIdCard  : "loadPage.htm?url=/collect/readIdCard.page",  // 进入读取身份证页面 
  member   : "loadPage.htm?url=/collect/member.page",   // 进入输入会员卡号页面 
  bankCard  : "loadPage.htm?url=/collect/bankCard.page",   // 进入插入银行卡页面 
  url   : "loadPage.htm?url=/collect/url.page"    // 进入跳转url页面 
 }, 
 
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:

var msg = ""; 
for(var key in Pin) { 
 for(var i in Pin[key]){ 
 msg+=i+": "+Pin[key][i]+"\n"; 
 } 
} 
alert(msg);