CoreJS: Functions as Objects

Functions are Objects too!

Begin with this function definition in the exercises below:

function paint(obj) {
    obj.color = 'red';
}

All functions are also objects, which has the following implications:

1) Functions can have aliases.

• Make an alias for paint and call that alias as a function.

2) Functions can be methods of objects.

• Convert paint into a method, so that it always paints its owner.

3) Functions can be arguments.

• Use paint as a callback with forEach on some array of objects.

• Use an anonymous function which paints things 'blue' as a callback to forEach.

4) Functions can have properties of their own.

• Use the length property to determine how many arguments function paint requires.

• Rewrite paint to use, instead of 'red', a property of itself called color. Then set that property to 'green'. Then paint something green.

5) Functions can have methods of their own.

• Give function paint a method which sets the color it uses to paint things. You should be able to use it like this:

paint.useColor('turquoise');
paint(obj); // --> sets obj's color to 'turquoise'

call and apply

• Use this paint function to change of color of both car and fence:

function paint(color) {
    this.color = color;
}
var car = {wheels:4}, fence = {length:20};

• Use Math.max to find the largest number in this array:

var nums = [9,5,8,2,4,11,8,2,7,1,0,99,25,3,6,42];

this pitfalls

There's a problem in the code below:

function talk() {
    console.log(this.noise);
}

var animals = [dog, cat, canary];
animals.allTalk = function() {
    this.forEach(talk);
}
animals.allTalk(); // failure!

Identify the problem and fix it! Rewrite the allTalk method of array animals to
make each animal talk. You must use function talk without changing its definition, and forEach(something). something should be a function which is not talk but instead somehow calls talk.

Instances and Factory functions

We know how to make animal instances by hand:

var dog = {
    name:'dog',
    noise:'woof',
    talk:function() {
        console.log(this.noise);
    }
}
var sheep = {
    name:'sheep',
    noise:'baaa',
    talk:function() {
        console.log(this.noise);
    }
}

Write a function to create any number of animals like those above.

Sharing Instance Methods

Write two versions of a factory which makes animal instances which all share a single copy of their talk method.

1. First implement talk as a global function.

2. Instead of using a global function, attach talk as a property of the factory itself, but expect it to be called through individual animals.

Samples

scratchpad

console

Diagrams