the-modern-javascript-bootcamp/notes/chapter4_javascript-functions.md

Chapter 4: JavaScript Functions

Function Basics

Simple JS function definition and invocation:

// Function Definition
let greetUser = function () {
    console.log('Welcome user!');
}

// Function Invocation
greetUser(); // => 'Welcome user!'

Simple JS function with 1 argument and return:

let square = function (input) {
    return input*input;
}

console.log(square(3)); // => 9

Undefined and Null

• undefined:
  • Senario 1 (Undefined for variable): when variable is declared but without assigning value. JS assign undefined to it.
  • Senario 2 (Undefined for function arguments): Function argument is undefined when no value is parsed. Program hence does not crash.
  • Senario 3 (Undefined as function return default value): When function code does not return anything and when it's invoked. It return undefined.
• null:
  • Emptiness assigned to a varaible: When a value is not sure and want to specify the variable is empty, developer can assign null.

Multiple Arguments and Argument Defaults

Defining functions with multi-arguments:

let func_name = function (arg1, arg2) {
    // function body
}

Invoke this function:

func_name(param1, param2);

Dafualt value of arguments can be set in function def:

// Default arguments
let getScoreText = function (name = 'Anonymous', score = 0) {
    console.log(name)
    console.log(score)
}

getScoreText() // 'Anonymous', 0

Function Scope

Local variable within function only exist in function scope

Template Strings

Template String (aka Template literals): string literal careted using backticket

`This is ${expression}`