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Using Javascript with HTML DOM
September 2023 (2239 Words, 13 Minutes)
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Home | HTML | JavaScript | DOM | Data Types | Correcting errors |
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>
<head>
<script>
function swapLinks() {
var link1 = document.getElementByID("link1");
var link2 = document.getElementByID("link2");
var text1 = link1.textContent;
var text2 = link2.textContent;
link1.href = href2;
link2.href = href1;
link1.textContent = text2;
link2.textContent = text1;
}
</script>
</head>
<body>
<header>
<div id="titles">
<h2>Demo Website</h2>
<h4>A website to host coding projects.</h4>
</div>
</header>
<p>
<div class="text">
<span class="paragraph" size=1>This is a sample paragraph</span><br>
<span class="paragraph"></span><br>
<span class="sentence" size=2>This is a sentence.</span>
<br>
<button id="random-button">Press to switch links</button>
</div>
</p>
<p>
<div class="links">
<a id="link1" href="https://www.w3schools.com/">W3 Schools</a>
<a id="link2" href="https://chat.openai.com">ChatGPT</a>
</div>
</p>
<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/2/2f/Google_2015_logo.svg/368px-Google_2015_logo.svg.png"/>
<br>
<img src="https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.computertechreviews.com%2Fwp-content%2Fuploads%2F2020%2F05%2FModern-Web-Design-Trends-1200x675.jpg&f=1&nofb=1"/>
<br>
<br>
</body>
</html>
Demo Website
A website to host coding projects.
This is a sample paragraph
This is a sentence.
This is a sentence.