study

A diary of some sort. An interesting one.

Lesson 2: Functions

This lesson, according to the instructors, generally reviews the new features and changes available to the ‘already powerful’ JS functions, plus new easier and less clunky ways to do some pretty important things.

On Arrow Functions

Arrow function expressions are now a thing, make judicious use of them where possible.

Here’s an illustration showing why using a arrow function (also known as fat arrow functions, just FYI) is more ‘convinient’ over the ‘normal’ way.

The normal way:

function getSquared(num) {
  return num * num;
}

getSquared(2); // returns 4

The new ‘fancy’ way:

const getSquared = num => num * num;

getSquared(3); // returns 9

See?

Less code.

Quick pointer though, arrow functions can be either written in a:

The concise body syntax format is what was illustrated above (where there’s no need to explicitly return the results). Using block body syntax, the return keyword is required.

What is this?

The value of this, according to the Udacity lessons, inside of an arrow function is the value of this outside of the arrow function.

I know this explanation of this isn’t clear enough, even for me, but I promise to do more brushing up in this area.

On Default Function Parameters

Take the following function declaration:

const amazingThings = (thing1, thing2) => `${thing1} and ${thing2} are amazing things!`;

Calling the function without passing in the exact required args result in something funny. Here:

amazingThings('Me');

//=> returns "Me and undefined are amazing things!"

Enter, default function params.

Using default function parameters, this can be conviniently circumvented. Here:

const amazingThings = (thing1 = 'Sleep', thing2 = 'Music') => `${thing1} and ${thing2} are amazing things!`;

amazingThings('Me');

//=> returns "Me and Music are amazing things!"

amazingThings('Me', 'You');

//=> returns "Me and You are amazing things!"

amazingthings();

//=> returns "Sleep and Music are amazing things!"

On Creating Javascript Classes

There’s now a Class keyword which can be used to make classes as thus:


class SuperHero {
  constructor(name, universe, powers) {
    this.name = name;
    this.universe = universe;
    this.powers = [...powers];
  }
}

To make an object using the prototype defined above:


const antman = new SuperHero('Antman', 'MCU', ['Sacarsm', 'Shrinkability', 'Ocassional Stupidness']);

antman.universe // returns MCU

Also, child classes can be created based existing parents using the extends keyword as follows:


class Child extends Parent {
  constructor () {
    super();
    // ....
  }

  // ...
}

The super() keyword seen above is used within the subclass to access properties present on the Parent class. Also worth pointing out is the fact that the super keyword can be used as both a function and an object within the subclass.

Finally, one must take note of the fact that in a subclass constructor, super() must be called before the this keyword can be used.