10 JavaScript Concepts That Every Developer Should Know.
By: Saiful Islam Sojib
Tags: JavaScript, Web Development, Programming, ES6

JavaScript ES6

Hi! Programmers, Today I will explore 10 javaScript Concepts That Every Developer Should Know. So, let’s go….

1. Arrow Function

An arrow function expression is an alternative way to declare a traditional function expression. But it has some difference between arrow function and traditional function.

Traditional functions have ‘this’ keyword but arrow functions have no ‘this’ keyword. Traditional functions have ‘arguments’ keywords but arrow functions have no ‘arguments’ keywords. Traditional functions can use as ‘constructors’ but arrow functions can not use as ‘constructors’.

If we use an arrow function, we should remove the function keyword and set arrow => between the argument and opening body bracket. We can store the function in a variable. If an arrow function writes in one line then we can remove body brackets and the return keyword. If the arrow function has only one argument, then we can remove argument parentheses.

Code Examples:

const sum = (a, b)=> {

return a+b;

}

console.log(sum(5, 7)) // output, 12 const multiply = (a, b) => a*b

console.log(multiply(5, 7)) // output, 35 const double = a => a*2

console.log(double(5)) // output, 10

2. Default parameters

You can use default parameters in a function after es6. If never pass the parameter then you can set a default parameter. The default parameter will set if you pass undefined or you didn't pass the parameter otherwise, it is not set.

Code Examples:

function add(a, b=5){

return a+b;

}

console.log(add(7)) // output, 12 function add(a, b=5){

return a+b;

}

console.log(add(7, 4)) // output, 11

3. IIFE Function

IIFE full meaning — Immediately Invoked Function Expression

If we defined a function and we want the function will call Immediately, then we can use the IIFE function. IIFE function is an anonymous function and the function will call Immediately. We can’t call the IIFE function another time.

Code Examples:

(function (){

console.log(5+7);

})(); // output, 12

4. Spread operator

Spread operator(…) or three dots are the es6 Features. You can concat array, object, and string by using the spread operator. It is used for array expression or string to be expanded or an object expression to be expanded in places. You can copy all the elements of an array, all the properties of an object, and all iterable of the string.

Code Examples:

const numbers = [1, 8, 5, 15, 10];

console.log([...numbers]) // output, [1, 8, 5, 15, 10]

console.log([...numbers, 65]) // output, [1, 8, 5, 15, 10, 65] const user = {name: 'Shuvo'}

console.log({...user}) // output, {name: 'Shuvo'}

console.log({...user, id: '1'}) // output, {name: 'Shuvo', id: '1'}

5. isNaN() Method

isNaN() Method returns true if the argument is NaN, Otherwise it returns false.

Code Examples:

console.log(isNaN(12)); // output, false

console.log(isNaN("false")); // output, true

console.log(isNaN("12")); // output, false

console.log(isNaN("")); // output, false

console.log(isNaN("12as")); // output, true

JavaScript has two types of data types. Primitive and Reference or Objects and Functions.

6. Primitive Values

There are 7 Primitive data types. They are___

Number String Boolean Undefined Null Symbol BigInt

Code Examples:

console.log(typeof(5)) //output, "number"

console.log(typeof('Hello')) //output, "string"

console.log(typeof(true)) //output, "boolean"

console.log(typeof(undefined)) //output, "undefined"

console.log(typeof(null)) //output, "object" **In JavaScript, typeof null is "object". We can consider it a bug in JavaScript and we can think it should be "null".

7. Reference or Objects and Functions

Without primitive data types, javaScript’s other data types are reference data types. They are ____

Object Function

Arrays, regular expressions, and dates are the Object type.

Code Examples:

console.log(typeof({name: 'Faysal'})) //output, "object"

console.log(typeof([1, 2, 5])) //output, "object"

console.log(typeof(() => 4+4)) //output, "function"

console.log(typeof(/exp/)) //output, "object"

8. Double Equal(==) vs Triple Equal (===)

In javaScript two double equal compare the values. If the value is equal, return true. But triple equal compare the values and compare the data type. If the value is equal and the type is equal, then return true, otherwise, return false. We should use triple equal to compare and it is best practice.

Code Examples:

console.log(5=="5") // output, true

console.log(5==="5") // output, false

console.log(1==true) // output, true

console.log(1===true) // output, false

console.log(0==false) // output, true

console.log(0===false) // output, false

9. Ternary Operator

Ternary Operator, another way to conditional checking. This is the smallest way for condition. You can write one line condition by using the ternary operator. In ternary operator conditional checking using a question mark (?) and a colon (:).First of all, we write the condition, num>5 then we should use a question mark (?), then we wire the code if the condition is true, then we should use a colon (:), then we wire the code if the condition is false. We can use nested conditions in the ternary operator. The ternary operator should write code the condition is true and false.

Code Examples:

const number1 = 5;

const number2 = 8;

const largest = number1 > number2 ? number1: number2;

console.log(largest) // output, 8

10. Destructuring

There are two Destructuring, Array and Object.

Object Destructuring: We can destructure object properties in variable and the variable name and property name should be the same. We can destructure any properties in an object. In object Destructuring, we should not maintain any order which property was first or last or any position. In object destructuring, we should declare a variable with curly braces { } . In curly braces, we should write those properties that we want to destructure from an object. Then we should use the assignment operator = and on the right side, we use that object.

Array Destructuring: We can destructure array elements in variable and the variable name and the element don't need to be the same name. In array destructuring, we should maintain the order which element was first or last or any position. In array destructuring, we should declare a variable with an array symbol [] . In the array symbol, we should write elements by an order which element was first or last or any position. If we want the second element and don’t want the first element we can use only a comma. Then we should use the assignment operator = and on the right side, we use that array.

** In Array and object destructuring we can use a spread operator or three dots to destructuring another array of elements in an array variable and another object properties in an object variable.

Code Examples: