Basics of Functions in JS

\ Here we will be going through the very basics of javascript. Functions are one of the core fundamental building blocks in javascript. Functions are like programs in your [programs. It](http://programs.It) is a block of code designed to perform a particular task. A javascript function can be executed when you invoke or call it any time you want, in the same way that Hermione gives a wave of her wand anytime she wants. ![hermione](https://cdn.hackernoon.com/images/cksi-6-ohna-001-c-0-as-66-tsubq-3-y.jpg) ## *__SYNTAX__* ```js function wingardiumLeviosa (parameter1, parameter2) { // code to be executed // make objects fly } wingardiumLeviosa(argument1, argument2) ``` \ JS Function is defined with the `function` keyword followed by its name and parentheses `()`. Parentheses may contain parameters. Inside the curly braces, the code to be executed is placed. The function is executed by invoking by its name with parentheses and arguments if any. \ * **Parameters** - Parameters are nothing but named variables passed into a function. * **Arguments** - The arguments are the values passed into a function. * **Code** - Code to be executed in the function placed inside the curly braces. * **Return** - Return statement ends the function and returns control to the calling function. It returns value to the calling function. \ Lets write a function `fullName` which takes `firstName` and `lastName` as arguments and returns full name of a person. \ ```js function fullName(firstName, lastName) { let fullName = `${firstName} ${lastName}`; return fullName; } ``` ## Invoking or Calling a Function You cannot execute a function by just defining it. For executing a function you need to invoke (call) a function. \ You can call a function by just its name with parentheses. \ ```js fullName(arg1, arg2) ``` \ The return value is stored in the calling function. You can log the value to the console by. \ ```js let a = fullName('Sankalp', 'Swami'); console.log(a); // will print: Sankalp Swami ``` \ Some examples - \ ```js let a = fullName('Harry', 'Potter'); let b = fullName('Hermione', 'Granger'); let c = fullName('Ronald', 'Weasley'); let d = fullName('Lord', 'Voldemort'); console.log(a); // will print: Harry Potter console.log(b); // will print: Hermione Granger console.log(c); // will print: Ronald Weasley console.log(d); // will print: You know who // just kidding ``` ## Argument Defaults When you have declared a parameter but nothing is passed as an argument you can set a parameter to default. \ ```js function fullName(firstName='-', lastName='-') { let fullName = `${firstName} ${lastName}`; return fullName; } ``` \ In the above example if one of the arguments is not passed, it gets a default value of `-`. \ ```js let a = fullName('Dobby'); console.log(a); // will print: Dobby - ``` ## Function Scope Functions create a new local scope. This contains variables defined in the function body as well as the arguments passed in the functions. \ ```js function add (num1, num2) { let result = num1 + num2; return result; }; console.log(add(2, 4)); console.log(num1); // ReferenceError: result is not defined ``` \ Here function `add` is defined at global scope but variable `num1` is passed as an argument inside the `add` function so, it is not accessible outside the function. \ Once a function is defined, it can be used over and over and over again. You can invoke the same function many times in your program, which saves a lot of your work. Thanks for reading, keep learning, Peace and Bubbyyee. ![Bubbyee](https://cdn.hackernoon.com/images/cksi-6-ohnb-001-d-0-as-60-u-79-hols.jpg)

Basics of Functions in JS

@sankalp1122
Sankalp Swami

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Basics of Functions in JS

@sankalp1122Sankalp Swami

Tags

@sankalp1122
Sankalp Swami