FunctionThis

Overview

The goal of this assignment is to see what this equals in the four class types of functions.

Understanding the this keyword in JavaScript is not easy. One step on the way is to see how it is treated in types of functions. The four basic types of functions are explained here and here.

Get started

Install phantomjs-prebuilt if you have not done so already:

npm install -g phantomjs-prebuilt

Then get the project from the elven-assignments repository:

cd ~/Git/elven-assignments
git pull
cp -rv FunctionThis/ ~/Git/prog272-XXX-2016/Week05-FunctionThis
cd ~/Git/prog272-XXX-2016/Week05-FunctionThis
npm install && bower install

Strict

In this example, set strict off. Do not use strict in any of the functions you implement in control.js unless I explicitly say to do so.

In Gruntfile.js have jshint ignore node_modules and components and set strict to false. Also add validthis:

jshint: {
    files: ['**/*.js'],

    options: {
        ignores: [
            '**/node_modules/**', '**/components/**'
        ],
        reporter: require('jshint-stylish'),
        strict: false,   // WE CHANGED THIS LINE TO FALSE
        validthis: true, // WE NEED THIS TOO
        jasmine: true
    }
},

Specs

Let’s look at some tests:

/**
 * Created by charlie on 10/7/15.
 */

describe('Elvenware Simple Plain Suite', function () {

    'use strict';

    it('expects true to be true', function () {
        expect(true).toBe(true);
    });

    it('expects getNine to return 9', function () {
        var result = getNine();
        expect(result).toBe(9);
    });

    it('expects a simple function called getThis to set this to the window object', function() {
        var result = getThis();
        expect(result).toBe(window);
    });

    it('expects a simple anonymous function to set this to the window object', function() {
        var result = getThisAnonymous();
        expect(result).toBe(window);
    });

    it('expects a method of myObject called getThis to set this to myObject', function() {
        var result = myObject.getThis();
        expect(result).toBe(myObject);
    });

    it('expects a method of myFunction called getThis to show this is myFunction', function() {
        var result = myFunction.getThis();
        expect(result).toBe(myFunction);
    });

    it('expects a constructor function called MyFunction to have a public method called getThis that shows this is MyFunction', function() {
        var myFunction = new MyFunction();
        var result = myFunction.getThis();
        expect(result).toBe(myFunction);
    });

    it('shows you can set the this operator for getThis to myObject', function() {
        var result = getThis.call(myObject);
        expect(result).toBe(myObject);
    });

    it('shows that return this from a simple strict function returns undefined', function() {
       var result = getThisStrict();
        expect(typeof result).toBe('undefined');
    });
});

Implement

In control.js we should implement some functions like this:

function getNine() {
    return 9;
}

function getThis() {  
    return this;
}

Notice that we are not using strict. You implement the remaining functions specified in the tests.

Turn it in

The usual.