intro.md

introduction

The difference between var and let

• When you use var, you can declare the same variable as many times as you like, but with let you can't. The following would work :

var myName = 'Chris';
var myName = 'Bob';

• But the following would throw an error on the second line:

let myName = 'Chris';
let myName = 'Bob';

• You'd have to do this instead:

let myName = 'Chris';
myName = 'Bob';

arrays

• An array is a single object that contains multiple values enclosed in square rackets and separated by commas.

let myNameArray = ['Chris', 'Bob', 'Jim'];
let myNumberArray = [10, 15, 40];

objects

• An object is a structure of code that models a real-life object. You can have a simple object that represents a box and contains information about its width, length, and height, or you could have an object that represents a person, and contains data about their name, height, weight, what language they speak, how to say hello to them, and more.

let dog = { name : 'Spot', breed : 'Dalmatian' };

dog.name

dynamic typing

• JavaScript is a "dynamically typed language", which means that, unlike some other languages, you don't need to specify what data type a variable will contain (numbers, strings, arrays, etc).

let myString = 'Hello';

let myNumber = '500';
typeof myNumber; // 'string'
myNumber = 500;
typeof myNumber; // 'number'

constants

• In javascript constant are define using the key word const this will be a value that once declared can't be changed.