How to debug Javascript errors

17th Nov 2017

It’s normal for you to make errors when you code. So if you see an error, you don’t have to be afraid. I get error messages all the time. When I have bad days, I get more error messages!

Error messages are something bad. We’re actually lucky to have error messages show up infront of us when code.

Think about designers and other professions, when they create something, its hard for them to know what’s wrong with their work.

In our case, we get instant feedback through error messages. These error messages are like angels that gently tell us that something is wrong. You can correct the code and your program would work.

Let’s go through an example.

In this code, we’re trying to add an event listener to a button, and when the button is clicked, the button should turn orange.

If you hit the refresh button, you’ll see an error message. The first thing you do is to breathe and relax.

Then, you read the error message. You also look at where the message occurs.

The error message says you can’t read a property addEventListener of null. If you’re unsure whether btn is null, you can do a console.log.

Here, you’ll understand you missed a . when declaring the btn variable. What you’ll need to do is fix this querySelector declaration and your code works.

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