JavaScript Data Types

Lena — Mon, 06 Mar 2023 04:10:01 +0000

Data Types refer to the types of data that can be stored in a variable. They include primitive and non-primitive data types.

The primitive data types are:

String
Number
Boolean
Undefined
Null
Symbol
The non-primitive data type is:

An object can be an array, function, date , object and Regex (Regular expression).

The major difference between the primitive and non-primitive data types is that in primitive data types, only one value can be stored while more than one value can be stored in the non-primitive type.

For the purpose of this post, we will only focus on string, number, boolean, undefined and null.

String

A group of characters surrounded by single quotes (‘’), double quotes(“”), backticks or String() method.

let str1 = 'String in single quote.';
let str2 = "String in double quote.";
let str3 = `String in backticks.`;
let str4 = String('Creating a string with String().');

Number

The number can be an integer (positive or negative), a floating point value, exponential value, Infinity or Nan (not a number).

const num1 = 1; // Positive integer
const num2 = -10; // Negative integer
const num3 = 24.3; // Floating point value
const num4 = 10e2; // Exponential value: 10*100
const num5 = 5 / 0; // Infinity
const num6 = 'hello' * 5; // Nan
let num7 = Number(10);
Num7 = Number(5);

Boolean

This is a logical data type that has two values true and false. It can be used for comparison of variables or to check a condition.

let checker = true;
const a =5, b = 9;
if (a < b) {
  // if a is less than b
  checker = true;
}
else {
  checker = false;
}
a == b; // a is equal to b returns false
a != b; // a is not equal to b returns true

Undefined

This type of data is a variable where the variable has been declared but remains undefined. A value has not been assigned.

let firstName; // Declaration
console.log(firstName); // Undefined
firstName = 'John'; // Assign the string John
console.log(firstName); // John

Null

The null data type refers to a value that means the value is absent or empty.

let x = null;
console.log(x) // null

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JavaScript Variables

Lena — Thu, 02 Mar 2023 17:41:39 +0000

They allow you to store data values in them for future use. Think about it this way, the variable is like a container where you can put a fruit. In the blue container, you can place an apple; in the yellow container, you can place an orange. When you need to find your orange, you refer to the yellow container.

Variables in JavaScript are declared using var, let or const.

var num;
let num1;
const num2; //Error. It must be initialized

The assignment operator = is used to give the variable a value. Note = does not mean equal to as in arithmetic.

The semicolon (;) is used in JavaScript like a sentence’s full stop (.). Did you see what I did there? 🙂

It indicates the end of that line of code. The code will run without the semicolon, but it is standard practice to include it.

The keyword var was used before 2015, and coding for older browsers

var x;
x = 1;
var y = 3;
var num = 100;

Variables can also be declared using a newer convention introduced in 2015, let and const

The keyword let is used if the value is likely to change.

let x;
x = 2;
let y = 24;
let num1 = 120;

The advisable method to declare a variable is using the keyword const. In this case, the value does not change.

const a = 3;
const b = 5;
const num2 = 150;

If you try to change the value of num2, it would result in an error.

num2 = 200 // Error

More than one variable can be declared on the same line of code.

let x = 1; y = 2; z = 3;

Alternatively, it can be written as such

let x, y, z;
x = 1;
y = 2;
z = 3;

Variable names can be simple or more elaborate. Ideally, they should be descriptive. It should describe the value stored in it. For example, if you want to store the price of an apple in a variable. Instead of declaring it as x, which is ambiguous.

const x = 1;

Use

const price = 1;

Even better

const priceOfApple = 1; // The variable is written in camelCase

Variables can store numbers, characters, strings or Boolean values. We will talk about these in the future. Let’s take a look at some more examples.

const firstName = 'John'; // String
let age = 24; // Integer
const loggedIn = true; // Boolean

Rules for naming variables:

They must start with a letter, an underscore (_) or the dollar sign ($)
They cannot begin with a number.
They are case-sensitive; A is not the same variable as a.
JavaScript uses camelCase.