Get at it!

get_at_it.js

// Public domain.
// Attribution welcome, but not required. -- Pyry Jahkola.


// What's the point in all this? To get the equivalent of CoffeeScript's
// (?.) operator into vanilla JavaScript.


// get(x, key1, key2, ...) -- Get the result of x[key1][key2]..., or undefined.
// Will short circuit if a key is not found.
function get(x) {
    var keys = Array.prototype.slice.call(arguments, 1);
    for (var i = 0; x !== undefined && i < keys.length; i++) {
        x = (x && x.hasOwnProperty(keys[i])) ? x[keys[i]] : undefined;
    }
    return x;
}

// at(x, path) -- Given path='a.b.c', return x['a']['b']['c'], or undefined.
function at(x, path) { return get.apply(null, [x].concat(path.split('.'))); }

// var g = it('a.b.c') -- Make a getter function g(x) to the given key path of x.
function it(path) { return function (x) { return at(x, path); }; }


// Examples:

var x = {x: 1, y: ['a', 'b', {'c': false, 'd': null}]};

get(x, 'x')         //=> 1
get(x, 'y')         //=> ['a', 'b', {'c': false, 'd': null}]
get(x, 'y', 2, 'c') //=> false
get(x, 'y', 2, 'd') //=> null
get(x, 'z')         //=> undefined
get(x, 'z', 0)      //=> undefined

at(x, 'x')     //=> 1
at(x, 'y')     //=> ['a', 'b', {'c': false, 'd': null}]
at(x, 'y.2.c') //=> false
at(x, 'y.2.d') //=> null
at(x, 'z')     //=> undefined
at(x, 'z.0')   //=> undefined

it('x')(x)     //=> 1
it('y')(x)     //=> ['a', 'b', {'c': false, 'd': null}]
it('y.2.c')(x) //=> false
it('y.2.d')(x) //=> null
it('z')(x)     //=> undefined
it('z.0')(x)   //=> undefined

// With `Array.map` or `_.map`, you can use `it` similarly as `_.pluck`:

var people = [
    { name: 'Practical', home: { material: 'bricks',  color: 'red' } },
    { name: 'Fiddler', home: { material: 'stricks', color: 'brown' } },
    { name: 'Fifer', home: { material: 'straws', color: 'yellow' } },
    { name: 'The Big Bad', food: 'pork' }
];

people.map(it('name')) //=> ['Practical', 'Fiddler', 'Fifer', 'The Big Bad']
people.map(it('home.color')) //=> ['red', 'brown', 'yellow', undefined]

_.pluck(people, 'name') //=> ['Practical', 'Fiddler', 'Fifer', 'The Big Bad']
_.map(people, it('name')) //=> ['Practical', 'Fiddler', 'Fifer', 'The Big Bad']
_.map(people, it('home.color')) //=> ['red', 'brown', 'yellow', undefined]