JavaScript object: access variable property by name as string

Question

If I have a javascript object that looks like below

var columns = {
  left: true,
  center : false,
  right : false
}

and I have a function that is passed both the object, and a property name like so

//should return false
var side = read_prop(columns, 'right');

what would the body of read_prop(object, property) look like?

Answer 1

You don't need a function for it - simply use the bracket notation:

var side = columns['right'];

This is equal to dot notation, var side = columns.right;, except the fact that right could also come from a variable, function return value, etc., when using bracket notation.

If you NEED a function for it, here it is:

function read_prop(obj, prop) {
    return obj[prop];
}

---

To answer some of the comments below that aren't directly related to the original question, nested objects can be referenced through multiple brackets. If you have a nested object like so:

var foo = { a: 1, b: 2, c: {x: 999, y:998, z: 997}};

you can access property x of c as follows:

var cx = foo['c']['x']

If a property is undefined, an attempt to reference it will return undefined (not null or false):

foo['c']['q'] === null
// returns false

foo['c']['q'] === false
// returns false

foo['c']['q'] === undefined
// returns true