Accessing Properties in object [duplicate]

Answer 1

1. A cool property is not defined on foo, so foo.cool is undefined. If you did foo.name, it would return kevin.

2. cool in foo[cool] is the one you defined in the line above it, so it is actually foo['name'], which is defined and has the value kevin.

Answer 2

In var foo = { name: 'kevin'}; You store an object or a dictionary to that variable... which is now a key-value pair... so you can access the value of an object using the key...

since its a key value pair... you can't access it using '.' operator... because foo is not a class... type of foo will be a dictionary or object...

so, to access the value you need to use the [] paranthesis...

Answer 3

You can access the properties either...

• Literally by their name: property.name

• Indirectly by an expression that evaluates to their name: property[expr].

Hence if the expression cool has value 'name', then foo[cool] is the same as foo['name'] or foo.name.

The brackets also allow for...

1) more complex expressions like foo["data_"+variable] to easily access fields named like data_something,
2) property names that aren't simple identifiers, for example you could say foo["I'm long!"].

I hope this explanation brightens things up for you.