oop - Accessing object properties in javascript using for loop? -

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consider following object:

var nyc = { fullname: "new york city", mayor: "bill de blasio", population: 8000000, boroughs: 5 };

when try access each of properties using loop:

for(var key in nyc){ console.log(nyc[key]); }

it returns correct output(property values), but...

for(var key in nyc){ console.log(nyc.key); }

this return "undefined" on 4 lines

why strange behavior, since both:

console.log(nyc.fullname); console.log(nyc['fullname']);

give same o/p.

nyc.key looks property name key, not property name in variable key. first example, nyc[key], correct way use property name variable.

in javascript, can access object properties using dot notation , property name literal (obj.foo), or brackets notation , property name string (obj["foo"]). in second case, can use expression string, including variable lookup. (in es6, can use symbols brackets notation, it's not relevant here.)


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