EcmaScript 6

Ecma script 6: OOP

ECMAScript 6 is also known as ES6 and ECMAScript 2015.

Some of the new features in ES6:

• JavaScript let

• JavaScript const

• JavaScript Arrow Functions

• JavaScript Classes

• Default parameter values

• Array.find()

• Array.findIndex()

• Exponentiation (**) (EcmaScript 2016)

let

The let statement allows you to declare a variable with block scope.

const

The const statement allows you to declare a constant (a JavaScript variable with a constant value).

Constants are similar to let variables, except that the value cannot be changed.

Arrow Functions

Arrow functions allows a short syntax for writing function expressions.

You don't need the function keyword, the return keyword, and the curly brackets.

// ES5
var x = function(x, y) {
   return x * y;
}

// ES6
const x = (x, y) => x * y;

Arrow functions do not have their own this. They are not well suited for defining object methods.

Arrow functions are not hoisted. They must be defined before they are used.

Using const is safer than using var, because a function expression is always constant value.

You can only omit the return keyword and the curly brackets if the function is a single statement. Because of this, it might be a good habit to always keep them:

const x = (x, y) => { return x * y };

Classes

ES6 introduced classes.

A class is a type of function, but instead of using the keyword function to initiate it, we use the keyword class, and the properties is assigned inside aconstructor() method.

Use the keyword class to create a class, and always add a constructor method.

The constructor method is called each time the class object is initialized.

class Car {
  constructor(brand) {
    this.carname = brand;
  }
}

Now you can create objects using the Car class (create an object called "mycar" based on the Car class):

class Car {
  constructor(brand) {
    this.carname = brand;
  }
}
mycar = new Car("Ford");

Default Parameter Values

ES6 allows function parameters to have default values.

function myFunction(x, y = 10) {
  // y is 10 if not passed or undefined
  return x + y;
}
myFunction(5); // will return 15

Array.find()

The find() method returns the value of the first array element that passes a test function.

This example finds (returns the value of ) the first element that is larger than 18:

var numbers = [4, 9, 16, 25, 29];
var first = numbers.find(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

• The item value

• The item index

• The array itself

Array.findIndex()

The findIndex() method returns the index of the first array element that passes a test function.

This example finds the index of the first element that is larger than 18:

var numbers = [4, 9, 16, 25, 29];
var first = numbers.findIndex(myFunction);

function myFunction(value, index, array) {
  return value > 18;
}

Note that the function takes 3 arguments:

• The item value

• The item index

• The array itself