What is reason of using ' [ ] ' notation to access javascript object members instead of dot notation? [duplicate]

First it can be dynamic with a string:

 var key = 'name'; person[key]; 

Second, it also supports other symbols that aren't supported

 var key = 'first-name'; person[key]; 

Here's a use case (having impossible property name)

var obj = {}; > undefined obj['first name'] = 'Ivan'; > "Ivan" obj['first name'] > "Ivan" obj.first\ name > SyntaxError: Unexpected token ILLEGAL obj.first name > SyntaxError: Unexpected identifier 

Here is a very good reason for using the brackets, where we're passing in the property name as a parameter:

function showProperty(propertyName) { alert(person[propertyName]); } showProperty('name'); showProperty('age'); 

Here is another good reason, where we can access the 'headers' property of request using dot-notation, but we can not access the 'Content-Type' property of request.headers using dot-notation, because it contains a -.

request.headers['Content-Type'] = 'text/html'; 

It's very usefully to use this notation in methods, where you send your attribute name as parameter for example.

var Obj = function(){ this.abc = function(){ alert("abc!!!"); }; this.qqq = function(){ alert("QQQ!!!"); }; } var showAlert = function(param){ var myObj = new Obj(); myObj[param](); }; showAlert('abc');