Can syntax errors be caught in JavaScript?

Question

MDN states:

A SyntaxError is thrown when the JavaScript engine encounters tokens or token order that does not conform to the syntax of the language when parsing code.

But if there's a syntax error, how could the program even run in the first place?

How can JavaScript syntax errors even be caught?

Answer 1

You cannot use try-catch blocks to handle syntax errors as they are thrown while the code is being parsed and not while it's running.

However you can use window.onerror and figure out that there's an error. You must ensure that the onerror function is defined in a separate script tag and not in the tag in which the error may be present!

Eg:

This will not work, because the script is yet to start running when the error is thrown:

<script>
  window.onerror = function (e) {
    console.log('Error: ', e);
  };
  console.log('a'');
</script>

This will work:

<script>
  window.onerror = function (e) {
    console.log('Error: ', e);
  };
</script>
<script>
  console.log('a'');
</script>

jsfiddle demo