FAQ: Advanced JSX - Event Listeners in JSX

This community-built FAQ covers the “Event Listeners in JSX” exercise from the lesson “Advanced JSX”.

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This exercise can be found in the following Codecademy content:

Web Development

Learn ReactJS: Part I

FAQs on the exercise Event Listeners in JSX

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Why are we not calling the function with braces.
it is {functionName} but not {functionName()}. Why?

Because that will call functionName() when the element is initiated and set the handler to whatever the function returns.

So if you make a function like this.

function functionName(){
  return function(){

That would work, but otherwise you just need to reference the function with functionName not actually call it on runtime with functionName() (unless you have a function within a function like above).


The image doesn’t seem to be changing to a puppy - even after I clicked run solution (see attached).

Aside from the fact that the provided solution doesn’t seem to be working (even after I ran the CA provided solution), I also have a follow up question:

  1. The question “Why don’t we set the event listener attribute value to a function call?” explains that we simply reference the function makeDoggy to avoid calling it on runtime, which makes sense.

But, since function makeDoggy(e) takes e as a parameter, what specifically is being passed to e when we reference the function makeDoggy by using <img src… onClick={makeDoggy}, without passing an argument?



I don’t understand this also.

So here’s my current understanding of what happens here:

When the user clicks the img element, the event listener onClick calls the associated event handler function makeDoggy.

When the event listener calls the event handler, it also passes a single argument - an event object that contains properties describing the event that occurred.

In our event handler function makeDoggy(e), the parameter e receives the event object (e is just a naming convention for receiving an event object argument for event-triggered functions).

Then within our event handler function, e.target references the DOM Element to which the event occurred, and setAttribute() is a method that we can use to change the DOM element’s attributes. It takes 2 arguments - the name of an attribute whose value is to be set, and the value of that attribute to be set.

Basically, the tl;dr as I understand it is that when an event listener is triggered, it calls the event handler function and also passes an event object to it.


Ahh the cat is reading “You don’t know JS”. He’s understands what’s important in life haha!