Dynamically creating JavaScript elements with event handlers

Editor’s note: This article was last updated by Kayode Adeniyi on 19 April 2023 to include information about the different types of event handlers provided by JavaScript, and the lifecycle of a JavaScript event. For more information, learn how to create custom events for your app in JavaScript.

In this article, we’ll look at how to dynamically create JavaScript elements and how to attach event handlers to the dynamically created JavaScript elements.

We’ll cover the following:

• What are events in JavaScript?
  • What are event handlers in JavaScript?
  • Event handlers vs. event listeners
• The different types of event handlers provided by JavaScript
  • Inline event handlers
  • Traditional event handlers
  • DOM level 0 event handlers
• The lifecycle of a JavaScript event
• Dynamically creating JavaScript Handlers and attaching event handlers
• The document.createElement() method
• Creating an element with JavaScript backtick strings
• Template literals

What are events in JavaScript?

In JavaScript, events are the actions or triggers that happen in the web browser, such as clicking on a button, scrolling down a page, or submitting a form. These events/triggers can be generated by the user or by the browser itself. After they are generated, they trigger a JavaScript code to perform a certain action in response.

Similarly, events in JavaScript are triggered by specific actions and can then trigger a response in the JavaScript code that’s listening for that particular event. The way a traffic light controls the flow of traffic at an intersection, events in JavaScript can control the behavior of code.

What are event handlers in JavaScript?

When an event inside the JavaScript is triggered, a piece of code is executed. That code, also known as the event handler, is usually wrapped up inside a function. The event handler is usually attached to an HTML element, and it waits for the execution of an event to happen on that element.

To understand this more clearly, let’s build on our traffic light analogy. Think of an event handler as a traffic cop at an intersection. The cop waits for certain events, such as a car running a red light, to take an action that is a response to that event, such as writing the driver a ticket.

Similarly, an event handler is “listening” for specific events to occur on an HTML element. When the action occurs, the events handler is triggered and takes action by executing the JavaScript code associated with it.

Event handlers vs. event listeners

Event handlers and event listeners perform similar, but not identical, tasks. The main difference between them is how they are attached to the HTML element. Event handlers are attached as attributes to the HTML element itself, while event listeners are attached using JavaScript.

The different types of event handlers provided by JavaScript

Millions of developers are actively using JavaScript and changing its ecosystem. As such, there are different types of event handlers provided by the JavaScript:

• Inline event handlers
• Traditional event handlers
• DOM level 0 event handlers

Let’s take a look at each of the handlers above to understand what functionalities they provide.

Inline event handlers

Inline event handlers can be added directly to the HTML element using the on attribute. The main benefit of using inline event handlers is their simplicity. Some examples of inline events are:

• onclick: This event is triggered when the HTML on which it is attached gets clicked by the user. This event handler executes the code specified in its attribute
• onsubmit: This event handler is triggered when a form is submitted. It also executes the code specified in its attributes
• onmouseover: This event is triggered when the user moves their mouse on the element on which it is attached

Traditional event handlers

Traditional event handlers are used in web development to attach event listeners to HTML elements. As every browser supports them and they have been in use for very long, their main benefit is their compatibility and flexibility.

The main difference between traditional event handlers and inline event handlers is the way they are attached to the code. Inline event handlers are attached directly with the HTML code whereas traditional event handlers are attached with HTML through a separate JavaScript code block.

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Some of the traditional event handlers are:

• onkeydown: This event is triggered and the code is executed when the user presses the down key on their keyboard
• onscroll: When a user scrolls through an HTML document, this event handler triggers the function
• onload: When all the resources of the HTML page are loaded, this event is triggered

DOM level 0 event handlers

DOM level 0 event handlers refer to the traditional approach that was used during the early days of the web. During this approach, we simply used to set a property on an HTML element that usually corresponds to the name of the event we want to listen for, and then we assign a function to it that gets called after the event occurs.

Some of the DOM level 0 event handlers are the same as what we have already discussed. The only difference is the way they get attached to the HTML code is different. DOM level 0 event handlers include:

• onload: This event is triggered when a webpage has finished loading
• onmouseout: This event is triggered when a user moves their mouse out of an element
• onsubmit: This event is triggered when a form is submitted

The lifecycle of a JavaScript event

When an event is triggered, there are three phases that the event flows through the DOM (Document Object Model). These phases are the capture phase, target phase, and bubbling phase.

Capture phase

During the capture phase, the event first moves from the top of the DOM hierarchy towards the target element.

Target phase

After the event reaches the target element, it triggers the event listener attached to that element. The target phase is the phase where the event actually happens.

Bubbling phase

After the target phase, the event bubbles up from the target element towards the top of the DOM hierarchy. It’s important to note that not all events go through all three phases. Some events only have a target phase, while others may skip the capture or bubbling phase. It depends on where the event was triggered.

Dynamically creating JavaScript handlers and attaching event handlers

In JavaScript, attaching event handlers on an element that is not yet created or does not exist on the page will throw an error. As a result, the event handler code won’t work.

For example:

In the example above, the btn class does not exist in our index.html page. Therefore, this will throw an error of addEventListener of null.

We can dynamically create an element in JavaScript and attach event handlers with these two methods.

The document.createElement() method

The document.createElement() method allows us to create the HTML elements by their tag names, like <div>, <p>,<img>, and <h1>.

When we create an element with document.createElement, it doesn’t appear on the page immediately. It is going to be stored in the JavaScript memory until it is injected in the DOM. In this article, we are going to create a simple dog profile.

We’ll dynamically create our elements, inject it to the DOM, and also attach event handlers. Follow the link to the live CodePen demo:

Here is our index.html with no element in its body. We are going to dynamically create the element from JavaScript, inject it into the DOM, and also attach event handlers to the dynamically created elements:

In our index.js, we used document.createElement() to dynamically create a new div. Then, we added a dog class to the div we created earlier.

The classList property is used to add, remove, and toggle CSS classes on an element. Next, we created an image tag with src and alt attributes. We also created the h2 tag and added text contents in it. Then, we added a new p element with a class of info that will contain more information about the dog.

Next, we’ll dynamically create a button with a class of btn. We’ll add text saying click here to read more. If you inspect your browser, you won’t see the div with a class of dog we created because we haven’t appended it yet to the DOM.

Now, we’ve dynamically created an element. The next question is: how do we inject it to the page? To inject it into the DOM, we are going to use the .appendChild() method to append the dynamically created elements.

If you inspect your console, you will see the dynamically created elements injected in your DOM. Now we can add event handlers. To attach event handlers to the dynamically created button, we need to select the button with a class of btn and add an event listener of click.

We’re saying that onclick of the button, the p tag with a class of moreInfo should display block. Here is the CSS code for styling the dog profile:

Creating an element with JavaScript backtick strings

JavaScript backtick strings are also known as template literals. According to MDN, template literals are string literals allowing embedded expressions. You can use multi-line strings and string interpolation features with them.

We are going to dynamically create an element with JavaScript template literals, inject them to the DOM, and also attach event handlers.

Check out this live demo at CodePen. Below is the screenshot of the dog profile before triggering the event that will happen after Click to read more about me is clicked:

Below is the screenshot of the site after the event gets triggered. Notice the difference, and observe how triggering the event transforms the DOM and reveals a new dev that was previously hidden and has text inside of it:

Now, we are going to create the dog profile we created earlier, but with a difference in the JavaScript file. Our HTML and CSS remains the same.

Template literals

In the template literals.js file, we declared newDog, and use template literals to create multiple elements in it. If you console.log(newDog), you will see the element created like a string in the console. Or, if you console.log(typeof newDog), it is going to return a string showing that it is not yet a DOM element.

Next, we are going to use document.createRange() to turn the string into a DOM element. Then, we call the createContextualFragment() method that leaves on the range. When you console.log myFragment, you will see a range of objects (a collection of elements, or part of HTML we can work with). Then, we append myFragment to the body of the page.

N.B., If you need to do things like add event listeners or change classes, we should put it in the DOM with a createcontextual fragment and then put it in the body or anywhere else in the page.

Next, we are selecting the button with a class of .btn where the users click to read more about the dog. If you console.log(btn), you find out that it is in the DOM because we have injected it to the DOM through the createContextual fragment.

Adding event handlers

We added an event listener of click, and called a showMore function. In the showMore function, we selected the class moreInfo. If you check on our css you find out that the text was set to display none. So now we are saying that onclick of the button, let the display none change to display block.

Congratulations! Our dog profile is complete. All elements were created dynamically, and the event handler of onclick was added to the dynamically created elements.

Conclusion

In this article, we explored the concepts of events, event listeners, and dynamically creating new JavaScript elements by using document.createElement and template literals. We also conveyed the different approaches that one can take while writing an event listener. Remember that each approach has its own pros and cons.

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