Types

JavaScript has seven different defined data-types:

1. boolean: Binary data-type. Only valid values are true or false.

2. null: keyword that denotes a null value. This is not 0. It is the absence of value

3. undefined: a data-type that has not been defined with a value.

4. number: a numerical data-type.

5. string: any combination of characters to be read as text.

6. symbol: used to make anonymous object properties.

7. object: a container which can hold multiple data-type values.

Examples of each

boolean

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

null

let x = null;
console.log(x); //null = no value;

undefined

let x;
console.log(x); //undefined - no value assigned

number

let x = 17;
console.log(x); //17

string

let x = 'Hello World!';
console.log(x); //Hello World!

symbol

const MY_KEY = Symbol();
const obj = {
    [MY_KEY]: 123
};

Object

let x = {
    hello: 'test',
    number: 13
};
console.log(x.hello); //'test'
console.log(x.number); //13

Dynamically-typed

JavaScript is a dynamically-typed language, meaning that variables aren't assigned a specific type. You can see this in action with the following example:

let x = 19;
console.log(x); //x
x = 'tree';
console.log(x); //'tree'
x = false;
console.log(x); //false

A single variable can be assigned multiple types, but only one type at any given time. Each time a value is assigned, it replaces the previous value.

File Location

    javascript-library
        └── 1-Fundamentals
            └── 1-Grammar-and-Types
                05-types.js <-- You are here

Practice

1. In types.js, create a variable for each type and print each to the console.

2. Create a new variable. Use the typeof keyword to print to the console:console.log(typeof x)

3. Change the value of that variable to a different data-type, then use typeof again.

4. What happens? How can this be utilized in a program?