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Lesson: 15 | Data Types

Notes
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Notes

Numbers:

JavaScript has only one type of numbers and can be written with or without decimals.

var x = 12;

document.write(x);

Output: 12

var y = 3.14;

document.write(y);

Output: 3.14

var y = 3.14;

document.write(typeof(y));

Output: number

Strings:

A string is a series of characters like "Will Smith".

Strings are written with single or double quotes.

document.write("Will Smith");

Output: Will Smith

document.write('Will Smith');

Output: Will Smith

let x = 'Will Smith';

document.write(typeof(x));

Output: string

Booleans:

Booleans can only have two values as true or false and often used in conditional testing.

let x = 12;
let y = 15;

document.write(x==y);

Output: false

let x = 12;
let y = 15;

document.write(typeof(x==y));

Output: boolean

JS Arrays:

JavaScript arrays are written with square brackets and separated with commas.

const primes = [2, 3, 5, 7];

primes is the name of the array. 2, 3, 5 and 7 are the items of the array.

Every item has an array index. Array indexes are zero-based, which means the first item is [0], second is [1], and so on.

JS Objects:

JavaScript objects are written with curly braces {}.

const user = {userName:"John", password:"12abA", role:"Admin"};

In the example above, username is the name and John is the value.

Undefined:

In JavaScript, a variable without a value, has the value undefined. The type is also undefined.

let x = undefined;

document.write(x);

Output: undefined

let x = undefined;

document.write(typeof(x));

Empty Elements:

let txt = "";

document.write(txt);

Output:

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