Cheat Sheet

HTML

Link a JavaScript file

<script src="script.js"></script>

Create a button that calls a function

<button onclick="myFunction()">My Function</button>

Create a text input

<input type="text" id="my-input" />

Create an image

<img src="http://example.com/urlToImage.png" />

JavaScript

Define a function

function myFunction(parameter1, parameter2...) {

}

Call a function

myFunction(argument1, argument2...);

Create a variable

let x = "new variable";

Set a variable

x = 5;

Increment the value of a variable by 1

x++;

Increment the value of a variable by any number (like 10)

// replace 10 with the desired number
x += 10;

Find the maximum of some variables

let count1 = 5;
let count2 = 9;
let count3 = 4;

let maximumCount = Math.max(count1, count2, count3);

Generate a random number between 1 and any number

let random = Math.ceil(Math.random()*10);

Display a message to the user

alert("This is a message");

Make a string with embedded expressions and linebreaks

let adjective = "good";
let noun = "statement";

let myMessage = `this is
a very ${adjective} message.
and it is a ${noun}.`;

alert(myMessage);

Will print:

this is
a very good message.
and it is a statement.

Ask a question to the user

let answer = prompt("This is a question");

Do something if a condition is true

let answer = "question";

if (answer === "Answer") {
    alert("Do something");
}

Will print nothing; condition is not met.

Do something if a condition is false

let answer = "Answer2";

if (answer === "Answer1") {
    alert("Do something");
} else if (answer === "Answer2") {
    alert("Do something else if");
} else {
    alert("Do something else");
}

Will print:

Do something else if

Get the value from an HTML text input

HTML

<input id="my-input" />

JavaScript

let textInput = document.querySelector("#my-input");
let textValue = textInput.value;

Create a new HTML element

let newParagraph = document.createElement("p");

Insert an HTML element into the body of the page

document.body.appendChild(newParagraph);

Insert an HTML element into another element

let myDiv = document.querySelector("#my-div");
myDiv.appendChild(newParagraph);

Set the text content of an HTML element

myParagraph.textContent = "New Text Content";

Set a CSS property of an HTML element

myParagraph.style.color = "red";

Change the background color of the whole page

document.body.style.background = "red";

Repeat code a certain number of times

// replace 10 with the desired number
for (let i = 0; i < 10; i++) {
    alert("Repeat");
}

Create a new array

let myArray = ["Item One", "Item Two", "Item Three"];

Access an array element by index

let myFirstElement = myArray[0];

Set an array element by index

myArray[0] = "New Item One";

Add an item to an array

myArray.push("Item Four");

Get the number of items in an array

let elementsCount = myArray.length;

Loop through each item in an array

for (let i = 0; i < myArray.length; i++) {
    let currentItem = myArray[i];
    alert(currentItem);
}