Disclaimer: All of the information below is provided from the W3Schools section for ECMAScript 6
ECMAScript 6 is also known as ES6 and ECMAScript 2015.
Some people call it JavaScript 6.
This documentation page will introduce some of the new features in ES6.
letconstArray.find()Array.findIndex()**) (EcmaScript
2016)
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
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 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 };
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.
A simple class definition for a class named "Car":
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");
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
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 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:
ES6 added 2 new methods to the Number object:
Number.isInteger()Number.isSafeInteger()
The Number.isInteger() method
returns true if the argument is an
integer.
Number.isInteger(10); // returns true
Number.isInteger(10.5); // returns false
A safe integer is an integer that can be exactly represented as a double precision number.
The Number.isSafeInteger() method
returns true if the argument is a
safe integer.
Number.isSafeInteger(10); // returns true
Number.isSafeInteger(12345678901234567890); // returns false
ES6 also added 2 new global number methods:
isFinite()isNan()
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 global isNaN() method returns
true if the argument is
NaN. Otherwise it returns
false:
isNaN("Hello"); // returns true
The exponentiation operator (**) raises the first operand to the power of the second operand.
var x = 5;
var z = x ** 2; // result is 25
x ** y produces the same result as
Math.pow(x,y):
var x = 5;
var z = Math.pow(x,2); // result is 25