JavaScript Interactive — a console crash course

4.1 Simple Objects

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>>>

var obj = { a: 'value', b: 123, c: null }

Object instances are basically ordered hash sets of named values (properties). See 1.2 Object Types for the built-in objects.

>>>

Object.keys(obj)

["a", "b", "c"]

Property names can be listed with the built-in Object.keys() function. See also 2.3 Loops & Iteration for iteration over object properties.

>>>

obj.a

"value"

Property value access is an O(1) operation, making any object a candidate lookup table. See 2.5 Property Access for alternative syntax and details.

>>>

obj.toString

function toString() {
    [native code]
}

All objects also have built-in non-enumerable properties that can only be accessed directly. See the Mozilla JavaScript Reference for a list of these, such as toString, valueOf, hasOwnProperty.

>>>

obj.toString()

"[object Object]"

The built-in toString() method works for all objects. But the default implementation isn't all that exciting.

>>>

{ a: 1 } === { a: 1 }

false

Also worth noting is that object instances are never equal unless it is actually the same instance.

>>>

JavaScript Interactive — a console crash course

4.1 Simple Objects

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