Basics Notebook

JavaScript Basics

Welcome to the starting line. Here we cover the absolute essentials of JavaScript: declaring variables with var, let, and const, and understanding the various operators available in the language.

Variables

IN [ ]

// var is function scoped
console.log(x); // prints undefined or value
var x =5;

IN [ ]

// let and const are block scoped
console.log(y); // error
let y =6;
const PI = 3.141592653589793; // unchangeable

Operators

== equal to value

=== !== equal/notequal to value and equal type

IN [6]

let a = 5;
let b = "5";

console.log("a == b: " + (a == b) + " and a === b: " + (a === b));

IN [17]

// Arithmetic operators
let x = 5;
let z = x ** 2; // same as Math.pow(5,2)
console.log("x: " + x + " and z: " + z);

IN [36]

// Bitwise XOR operator
let a = 5, b = 3;
a = a ^ b;
b = a ^ b;
a = a ^ b;
console.log("a: " + a + " and b: " + b);

IN [1]

// isNaN(), Infinity (or -Infinity) are numbers
console.log(
  " isNaN('10') = " + isNaN("10") +
  "\n isNaN('John') = " + isNaN("John")+
  "\n typeof NaN = " + typeof NaN+
  "\n typeof Infinity = " + typeof Infinity+
  "\n typeof -Infinity = " + typeof -Infinity+
  "\n 5*Infinity = " + 5*Infinity+
  "\n 5/0 = " + 5/0
)