DOM • 17 min read

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.log the 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

<p id="e">I am a very cool guy</p>
<button id="buttonID" onclick="linkswitch()">Click here!</button>
<div>
    <p>I love my life</p>
    <p>I am in eleventh grade</p>
</div>

<a id="tlink" href="https://nighthawkcoders.github.io/teacher//2023/09/12/unit-1-summary.html">Teacher Website</a>
<a id="mlink" href="https://th35py27.github.io/CSP/">My website</a>

<p>I love CSP</p>

<div>
    <p>I love HTML</p>
    <p>I love divs</p>
</div>

<script>
    function linkswitch() {
        var link1 = document.getElementById("tlink");
        link1.innerHTML = "<a href='https://th35py27.github.io/CSP/'>Teacher Website</a>";
        var link2 = document.getElementById("mlink");
        link2.innerHTML = "<a href='https://nighthawkcoders.github.io/teacher//2023/09/12/unit-1-summary.html'>My Website</a>";
        var text1 = document.getElementById("e");
        text1.innerHTML = "<p>Links Switched!</p>";
    }
</script>