title: Using Javascript with HTML DOM hide: True description: A Tech Talk on how javascript can interact with HTML DOM type: ccc permalink: /basics/dom author: Rohan Juneja —
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Home | HTML | Data Types | DOM | JavaScript | JS Debugging |
Following along
Remember to “git pull” on teacher repository to update to lates.
- Run this notebook in VSCode
- Activate Help-Toogel Developer Tools to add console outputs to runtime experience
Referencing HTML elements using javascript
- To get an HTML element, use
document.getElementById("idTag") - You will use the ID that you set in your HTML
- if you
console.logthe resulting variable you will get some information about the element
%%html
<!-- the ID must be specified within the element -->
<h1 id="domTitleID">My Title</h1>
<!-- javascript goes here -->
<script>
var titleElement = document.getElementById("domTitleID")
<!-- outputs h1 tag -->
console.log("Example #1, show element in DOM")
console.log(titleElement)
</script>
Getting the data within the HTML element
- The variable titleElement stores the “object”
- Basically think of this as the group of data enclosed in HTML tag
- To access a certain type of data from an “object” we use “.” notation
- .innerHTML gets data within center of tag
%%html
<!-- the ID must be specified within the element -->
<h1 id="domTitleIDget">My Title</h1>
<!-- javascript goes here -->
<script>
var titleElement = document.getElementById("domTitleIDget")
<!-- outputs h1 innerHTML from h1 tag -->
console.log("Example #2, show innerHTML")
console.log(titleElement.innerHTML)
</script>
Setting the data within the HTML Element
- The innerHTML data in this “object” can be set like a variable
- Change the value of the innerHTML using the “=” (assignment) operator
%%html
<!-- the ID must be specified on the element -->
<h1 id="domTitleIDset">My Title</h1>
<!-- javascript goes here -->
<script>
var titleElement = document.getElementById("domTitleIDset")
titleElement.innerHTML = "Set and Update My Title"
<!-- outputs h1 innerHTML after h1 tag has been updated -->
console.log("Example #3, update innerHTML")
console.log(titleElement.innerHTML)
</script>
Creating elements
- Create a new element with the document.createElement function -> takes in the type of element
- Set properties in the element just like the “h1” example
%%html
<!-- the ID must be specified on the element -->
<div id="divContainerID">
<h1 id="h1ElementID">My Title</h1>
</div>
<!-- javascript goes here -->
<script>
// creates a new element
var pElement = document.createElement("p")
pElement.innerHTML = "Starting a paragraph of text."
// outputs p tag after it has been created
console.log("Example #4, create a p tag within JS")
console.log(pElement)
</script>
Issue! How to Create element that appears in HTML?
- Here is a visualization of what is happening => the “p” is not placed inside the HRML page!
Solution
- Correct by placeing the element somewhere in the page
- For example, we could add the element within the div
- For this, use the appendChild function on the div object (the parameter would be the p element we created)
- Remember, use the getELementById to get the object for something in the html (the div!)
- Updated Diagram
%%html
<!-- the ID must be specified on the element -->
<div id="divContainerIDset">
<h1 id="h1ElementIDset">My Title</h1>
</div>
<!-- javascript goes here -->
<script>
// creates a new element
var pElement = document.createElement("p")
pElement.innerHTML = "Starting a paragraph of text."
// outputs p tag after it has been created
console.log("Example #5, add p tag to HTML")
console.log(pElement)
// place the p element inside the HTML page
var div = document.getElementById("divContainerIDset")
div.appendChild(pElement)
</script>
Functions in JavaScript, using with DOM
- Functions allow you to “do something”
- ex. “eat food” in a Snake Game
- Functions were used in previous examples
- console.log = “print something”
- document.getElementById = “find an element with id”
- Functions take in parameters, what to do (inside the parenthesis)
- the parameter tells console.log what to print
- the parameter in document.getElementById tells the id of the element
- Functions can be used with DOM as well, thes will be shown below
Creeating functions
- document functions functions were used to create a lot of functionality, but how can a developer create their own?
- function are useful to avoid writing the same code over and over again
- function can contain parameters for input (they effectively become variables)
- function can contain a return, the are the “output” of the function
%%html
<!-- the ID must be specified on the element -->
<div id="divContainerIDfunction">
<h1 id="h1ElementIDfunction">My Title</h1>
</div>
<!-- javascript goew here -->
<script>
// define a function => takes parameter text, returns a new p tab
function createPTag(text) {
// creates a new element
var pElement = document.createElement("p")
// using the parameter like a variable
pElement.innerHTML = text
// outputs p tag after it has been created
console.log("Example #6, add p tag using a function")
console.log(pElement)
return pElement;
}
// using a function to create p tag
var pTag = createPTag("Starting a paragraph with cooler text than before.")
// place the p element in the webpage
var div = document.getElementById("divContainerIDfunction")
div.appendChild(pTag)
</script>
OnClick Event
- Run a function when an event occurs
- In this case, the p tag is created when the button is clicked
%%html
<!-- the ID must be specified on the elements -->
<button id="buttonID">Click here!</button>
<div id="divContainerIDbutton">
<h1 id="h1ElementIDbutton">My Title</h1>
</div>
<!-- our javascript goe here -->
<script>
// define a function => takes parameter text, returns a new p tab
function createPTag(text) {
// creates a new element
var pElement = document.createElement("p")
// using the parameter like a variable
pElement.innerHTML = text
// outputs p tag after it has been created
console.log("Example #7.1, add p tag using a function")
console.log(pElement)
return pElement;
}
// create a function that sets specific text and adds to div
function addPTagOnButton() {
// using our new function
var pTag = createPTag("Starting a paragraph with text created on button press.")
// place the p element in the webpage
var div = document.getElementById("divContainerIDbutton")
// add p tag to the div
div.appendChild(pTag)
// outputs p tag after it has been created
console.log("Example #7.2, update container adding a 'p' tag")
console.log(div)
}
// add the P tag when our button is clicked
var myButton = document.getElementById("buttonID")
myButton.onclick = addPTagOnButton
</script>
Hacks
- Copy your HTML code from the HTML hacks. Write a Javascript snippet to switch the links of the two a tags when a button is pressed. Once they are switched, change the inner HTML of the top p tag to the word “switched!”
%%html
<!-- html code goes here (make sure to run) -->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Stacked Boxes with Links</title>
<style>
/* CSS for the container */
.container {
display: flex;
flex-direction: column;
align-items: flex-start;
}
/* CSS for the main boxes */
.box {
width: 300px;
height: 150px;
border: 1px solid #000;
margin: 10px;
display: flex;
flex-direction: column;
justify-content: space-between;
padding: 10px;
background-color: #3a3a3a; /* Background color for the main boxes */
}
/* CSS for the smaller boxes inside */
.small-box {
flex-grow: 1;
border: 1px solid #f3f3f3;
margin: 5px;
display: flex;
align-items: center;
justify-content: center;
background-color: #3a3a3a; /* Background color for the smaller boxes */
}
/* Specific positioning for the top box */
.top-box {
width: 300px;
height: 75px; /* Adjusted height of the top box */
}
/* Specific positioning for the bottom box */
.bottom-box {
width: 300px;
height: 75px; /* Adjusted height of the bottom box */
}
/* Smaller box within the top box (Link 1) */
.top-small-box:nth-child(1) {
flex-grow: 1;
width: 33.33%; /* Adjusted width for Link 1 (1/3rd) */
height: 30px; /* Adjusted height of the top small box */
}
/* Smaller box within the bottom box (Link 4) */
.bottom-small-box:nth-child(1) {
flex-grow: 1;
width: 100%;
height: 40px; /* Adjusted height of the bottom small box */
}
/* Smaller box within the top box (Link 2) */
.top-small-box:nth-child(2) {
flex-grow: 1;
width: 33.33%; /* Adjusted width for Link 2 (1/3rd) */
height: 30px; /* Adjusted height of the top small box */
}
/* Smaller box within the bottom box (Link 5) */
.bottom-small-box:nth-child(2) {
flex-grow: 1;
width: 33.33%; /* Adjusted width for Link 5 (1/3rd) */
height: 40px; /* Adjusted height of the bottom small box */
}
/* Smaller box within the top box (Link 3, reverted to previous width) */
.top-small-box:nth-child(3) {
flex-grow: 1;
width: 100%; /* Reverted width for Link 3 */
height: 30px; /* Adjusted height of the top small box */
}
/* Links within the smaller boxes */
.small-box a {
text-decoration: none;
color: #a693ff;
font-weight: bold;
}
</style>
</head>
<body>
<div class="container">
<!-- Bottom Box (Flipped to the top) -->
<div class="box bottom-box">
<div class="small-box bottom-small-box">
<a href="#">P </a>
</div>
<div class="small-box bottom-small-box">
<a href="#">Button 1 </a>
</div>
</div>
<!-- Top Box (Flipped to the bottom) -->
<div class="box top-box">
<div class="small-box top-small-box">
<a href="#">A</a>
</div>
<div class="small-box top-small-box">
<a href="#">A</</a>
</div>
<div class="small-box top-small-box">
<a href="#">P</a>
</div>
</div>
</div>
</body>
</html>
<!-- put your HTML code in this cell, Make sure to press the Run button to see your results below -->
<script>
// put your javascript code here
// Generate random values for a and b between 1 and 10
var a = Math.floor(Math.random() * 10) + 1;
var b = Math.floor(Math.random() * 10) + 1;
console.log("a =", a);
console.log("b =", b);
if (a > b) {
console.log("a is greater");
} else if (b > a) {
console.log("b is greater");
} else {
console.log("both are equal");
}
</script>
<!DOCTYPE html>