Question

In javascript tutorial I’ve see the next object definition:

var myObject = {
    validIdentifier: 123,
    'some string': 456,
    99999: 789
};

What the purpose of such key-value pairs with quoted ones as keys? How one could operate with such values?

Answer 1

You can access them with brackets (called “bracket notation” or the “subscript operator”):

myObject['some string']

Keys like this must to be quoted because of the space (to avoid syntax errors).

The reasons for doing this are up to the developer. One (of like, a million) examples would be Backbone.js‘s delegateEvents that maps events and selectors to handler functions.