ECMAScript 6

What is ECMAScript 6?

ECMAScript 6 is also known as ES6 and ECMAScript 2015.

Some people call it JavaScript 6.

This chapter will introduce 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)

Browser Support for ES6 (ECMAScript 2015)

Safari 10 and Edge 14 were the first browsers to fully support ES6:

Chrome	Edge	Firefox	Safari	Opera
Chrome 58	Edge 14	Firefox 54	Safari 10	Opera 55
Jan 2017	Aug 2016	Mar 2017	Jul 2016	Aug 2018

JavaScript let

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

var x = 10;
// Here x is 10
{
  let x = 2;
  // Here x is 2
}
// Here x is 10

JavaScript 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.

var x = 10;
// Here x is 10
{
  const x = 2;
  // Here x is 2
}
// Here x is 10

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;

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Arrow Functions</h2>

<p>With arrow functions, you don't have to type the function keyword, the return keyword, and the curly brackets.</p>

<p>Arrow functions are not supported in IE11 or earlier.</p>

<p id="demo"></p>

<script>
const x = (x, y) => x * y;
document.getElementById("demo").innerHTML = x(5, 5);
</script>

</body>
</html>

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 are assigned inside a constructor() 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;
  }
}

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Class</h2>

<p>In this example we demonstrate a simple class definition and how to use it.</p>

<p id="demo"></p>

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

mycar = new Car("Ford");

document.getElementById("demo").innerHTML = mycar.carname;
</script>

</body>
</html>

Default Parameter Values

ES6 allows function parameters to have default values.

<!DOCTYPE html>
<html>
<body>

<h2>Default Parameter Values</h2>

<p id="demo"></p>

<script>
function myFunction(x, y = 10) {
  // y is 10 if not passed or undefined
  return x + y;
}
document.getElementById("demo").innerHTML = myFunction(5);
</script>

</body>
</html>

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:

Note that the function takes 3 arguments:

The item value
The item index
The array itself

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Array.find()</h2>

<p id="demo"></p>

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

document.getElementById("demo").innerHTML = "First number over 18 is " + first;

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

</body>
</html>

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:

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Array.findIndex()</h2>

<p id="demo"></p>

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

document.getElementById("demo").innerHTML = "First number over 18 has index " + first;

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

</body>
</html>

New Number Properties

ES6 added the following properties to the Number object:

EPSILON 2.220446049250313e-16
MIN_SAFE_INTEGER -9007199254740991
MAX_SAFE_INTEGER 9007199254740991

New Number Methods

ES6 added 2 new methods to the Number object:

Number.isInteger()
Number.isSafeInteger()

New Global Methods

ES6 also added 2 new global number methods:

isFinite()
isNaN()

The isFinite() Method

The global isFinite() method returns false if the argument is Infinity or NaN.

Otherwise it returns true:

isFinite(10/0);       // returns false
isFinite(10/1);       // returns true

The isNaN() Method

The global isNaN() method returns true if the argument is NaN. Otherwise it returns false:

isNaN("Hello");       // returns true

Exponentiation Operator

The exponentiation operator (**) raises the first operand to the power of the second operand.

x ** y produces the same result as Math.pow(x,y):

var x = 5;
var z = x ** 2;          // result is 25

var x = 5;
var z = Math.pow(x,2);   // result is 25

Source : https://www.w3schools.com/js/js_es6.asp

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