Free JavaScript course. Sign Up for tracking progress →

JavaScript: Syntax errors

If a JavaScript program is syntactically incorrect, the interpreter will show a relevant message and a message showing the file and line where the error might have occurred. Syntax errors occur when the code has grammatical mistakes. Grammar is essential to human language, but a text with grammar mistakes can still be read and understood. However, when it comes to programming, things are much more strict. Even a tiny mistake can mean your program won't run. Maybe you've mixed up your brackets, or there's a ; that you forgot to add — these are just some examples of such mistakes.

Here is an example of some code with a syntax error:

console.log('Hodor'

If we run this code we will see the following message: SyntaxError: missing ) after the argument list. In JavaScript, these errors are labelled as "SyntaxError". For technical reasons, this code running on code-basics won't show a message with a line and file. You can check this output on repl.it.

On the one hand, syntax errors are the most obvious because they deal with code grammar rules and have nothing to do with its logic. You can easily fix it once you find it.

On the other hand, an interpreter will not always tell you the correct position of an error. Sometimes you need to add a forgotten bracket to different place than what the error message says.

Instructions

This task isn't directly related to the lesson, but it would be useful to practice printing anyway.

Print the following text What Is Dead May Never Die.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

Tips

Definitions

  • Syntax errors - are grammar mistakes in a programming language.

  • SyntaxError (Parse error) - is a type of error in JavaScript which occurs when there are syntax errors in the code.


If you got stuck and don't know what to do, you can ask a question in our huge and friendly community