JavaScript Fundamentals

5. Variables

Variables allow us to store values.

Modern JavaScript mainly uses let and const.

let score = 10;
const name = "Daffa";

Use const when the variable should not be reassigned.

const name = "Daffa";

Use let when the value needs to change.

let score = 0;

score = 10;
score = 20;

For beginners, a simple rule is:

Use const by default. Use let when you know the value needs to change.

6. Basic Data Types

JavaScript has several basic types of values.

String

A string represents text.

const name = "Daffa";

Number

A number represents numeric values.

const age = 20;
const price = 15000;

Boolean

A boolean represents either true or false.

const isStudent = true;

These values are commonly used together when writing program logic.

7. Operators

JavaScript supports common mathematical operators.

10 + 5
10 - 5
10 * 5
10 / 5

There are also comparison operators:

10 > 5
10 < 5
10 >= 5
10 <= 5
10 === 10
10 !== 5

The result of a comparison is a boolean:

10 > 5

returns:

true

while:

10 < 5

returns:

false

These comparisons become especially useful with if statements.

8. Conditions

An if statement allows JavaScript to make decisions.

const score = 80;

if (score >= 50) {
    console.log("Pass");
}

We can add another case with else.

const score = 40;

if (score >= 50) {
    console.log("Pass");
} else {
    console.log("Fail");
}

We can also check multiple conditions:

const score = 80;

if (score >= 90) {
    console.log("A");
} else if (score >= 80) {
    console.log("B");
} else if (score >= 70) {
    console.log("C");
} else {
    console.log("D");
}

This is the basic mechanism we will use to build the game later.

9. Getting User Input

The browser provides a simple function called prompt().

const choice = prompt("Choose rock, paper, or scissors:");

The browser will display an input dialog.

Whatever the user enters is returned by prompt().

For example, if the user enters:

rock

then:

choice

contains:

rock

We can then use that value in our program.

For example:

const name = prompt("What is your name?");

alert("Hello, " + name);

If the user enters Daffa, the browser displays:

Hello, Daffa