object - JavaScript and square bracket notation -


i new in java script. in both of books: http://www.larryullman.com/books/modern-javascript-develop-and-design , http://www.packtpub.com/object-oriented-javascript/book both authors saying notation: object[unknownyetproperty] should work when have object , variable objects future property. problem 2 others notation works object['unknownyetproperty'] , object.unknownyetproperty not first one. 

var a1 = 'spring'; var a2 = 'autumn'; var a3 = 'summer';  var object = {     propertya1 : a1, // according books should work :-/     propertya2 : a2,     propertya3 : a3 }  console.log(object[propertya1] + ' ' + object['propertya2'] + ' ' + object.propertya3);

the working example: http://jsfiddle.net/cachaito/p78le

could explain me?

propertyal doesn't exist. reason string literal , dot notation work because correctly accessing properties of object. in first one, trying access object[undefined] because propertya1 isn't defined.


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