Following allong

Create a new markdown file in _posts (you will be able to put HTML in here)
You can try the concepts we are doing here on that post

Getting HTML elements in your javascript

To get an HTML element, use document.getElementById("the id here")
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 on the element -->
<h1 id="title1">My Title</h1>

<!-- our javascript goe here -->
<script>
var titleElement = document.getElementById("title1")
console.log("Example #1")
console.log(titleElement)
</script>

My Title

Basics of Objects

Our variable titleElement stores an “object”
Basically think of this as a group of data
- Example “name” is a variable
- BUT Student #10’s name is more specific, in this case Student #10 is the object
- The name of Student #10 would be referred to as Student #10.name rather than name
To access a certain type of data from an “object” we use “.” notation
- ie. To get the content of this titleElement, we would do titleElement.innerHTML

%%html
<!-- the ID must be specified on the element -->
<h1 id="title2">My Title</h1>

<!-- our javascript goe here -->
<script>
var titleElement = document.getElementById("title2")
console.log("Example #2")
console.log(titleElement.innerHTML)
</script>

My Title

Modifying the HTML

We can treat the data in this “object” (the html element) as a variable
- Therefore, we can change the value using the “=” (assignment) operator

%%html
<!-- the ID must be specified on the element -->
<h1 id="title3">My Title</h1>

<!-- our javascript goe here -->
<script>
var titleElement = document.getElementById("title3")
titleElement.innerHTML = "A better title"
</script>

My Title

Functions with Objects

Functions allow you to “do something”
- ex. “eat food”
We have used functions in a few of the examples
- console.log = “print something”
- document.getElementById = “find an element with id”
Functions take in parameters, what to do (inside the parenthesis)
- ex. we have to tell console.log what to print
- ex #2. we have to tell document.getElementById what the id of the elemt is
Functions can be used with objects as well
- Example: doWork (who is doing the work)
- With Objects: Student #10, doWork (Student #10.doWork())
- The parenthesis after indicate it is a function (parameters can go in there as well)

Creating elements

We can create an element with the document.createElement function -> takes in the type of element
We can set properties in the element just like we did with the h1

%%html
<!-- the ID must be specified on the element -->
<div id="container1">
    <h1 id="title10">My Title</h1>
</div>

<!-- our javascript goe here -->
<script>
   // creates a new element
   var pElement = document.createElement("p")
   pElement.innerHTML = "some text"
</script>

My Title

Issue!

We don’t see the element
Here is a visualization of what is happening => the “p” is not placed inside the page!

Solution

We need to place the element somewhere
For example, we could add the element to the div
- For this, we use the appendChild function on the div object (the parameter would be the p element we created)
- Remember, we can use 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="container2">
    <h1 id="title11">My Title</h1>
</div>

<!-- our javascript goe here -->
<script>
   // creates a new element
   var pElement = document.createElement("p")
   pElement.innerHTML = "some text"

   // place the p element in the webpage
   var div = document.getElementById("container2")
   div.appendChild(pElement)
</script>

My Title

Creeating functions

We were using functions for a lot of this functionality, but how can we create our own?
Useful to avoid writing the same code over and over again
We define parameters (they effectively become variables), and return “output” of the function
- ie. getStudent(name); parameters = name; returns the actual student
See the example below

%%html
<!-- the ID must be specified on the element -->
<div id="container5">
    <h1 id="title15">My Title</h1>
</div>

<!-- our javascript goe here -->
<script>
    // create a function => takes in text, returns created p
    function createPTag(text) {
        // creates a new element
        var pElement = document.createElement("p")

        // using the parameter like a variable
        pElement.innerHTML = text

        return pElement;
    }

    // using our new function
    var pTag = createPTag("cooler text")

    // place the p element in the webpage
    var div = document.getElementById("container5")
    div.appendChild(pTag)
</script>

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Reactivity

We can run functions when an event happens
- In this case, we will add the p tag when the button is clicked

%%html
<!-- the ID must be specified on the elements -->
<button id="myButton">Click here!</button>

<div id="myContainer">
    <h1 id="myTitle">My Title</h1>
</div>

<!-- our javascript goe here -->
<script>
    // create a function => takes in text, returns created p
    function createPTag(text) {
        // creates a new element
        var pElement = document.createElement("p")

        // using the parameter like a variable
        pElement.innerHTML = text

        return pElement;
    }

    // create a function that sets specific text and adds to div
    function addCoolPTag() {
        // using our new function
        var pTag = createPTag("cooler text")

        // place the p element in the webpage
        var div = document.getElementById("myContainer")

        // add p tag to the div
        div.appendChild(pTag)
    }

    // add the P tag when our button is clicked
    var myButton = document.getElementById("myButton")

    // using the onclick variable of the button
    // functions can be used as values for these variables
    myButton.onclick = addCoolPTag
</script>

My Title

%%html
<style>
    .div{
        border: 2px solid black;
        background-color: white;
    }
    .p{
        color: black;
        text-align: left;
    }
    .button{
        color: black;
        background-color: grey;
        border: 1px solid, dimgrey;
        border-radius: 2px;
    }
    .a{
        color: blue;
        text-align: left;
    }
</style>

<div class="div">
    <p class="p" id="text">Hi</p>
    <br>
    <button class="button" onclick="Switch()">Switch the links</button>
</div>
<div class="div">
    <a class="a" id="link1" href="https://frogpants.github.io/student/">Spencer's Page</a>
    <br>
    <a class="a" id="link2" href="https://seannakagawa.github.io/student/">Sean's Page</a>
    <br>
    <a class="a" id="link3" href="https://zafeera123.github.io/ZafeerA123/">Zafeer's Page</a>
    <br>
    <a class="a" id="link4" href="https://trystan-schmits.github.io/Student1/">Trystan's Page</a>
    <br>
    <p class="p">Links to be switched ^</p>
</div>

<script>

    let current = 0;
    function Switch() {
        current = (current+1)%2;
        var link1 = document.getElementById("link1"); //get link1
        var link2 = document.getElementById("link2"); //get link2

        var link1Html = link1.innerHTML; //get current htmls
        var link2Html = link2.innerHTML;

        link1.innerHTML = link2Html; //switch them
        link2.innerHTML = link1Html;


        document.getElementById("text").innerText = "Switched! state:"+String(current); //update paragraph
    }

</script>

Spencer's Page
Sean's Page
Zafeer's Page
Trystan's Page

Links to be switched ^

Using Javascript with HTML DOM • 17 min read

Description

Following allong

Getting HTML elements in your javascript

My Title

Basics of Objects

My Title

Modifying the HTML

My Title

Functions with Objects

Creating elements

My Title

Issue!

Solution

My Title

Creeating functions

My Title

Reactivity

My Title