The JavaScript exception "illegal character" occurs when there is an invalid or unexpected token that doesn't belong at this position in the code.
Message
SyntaxError: Invalid character (Edge)
SyntaxError: illegal character (Firefox)
SyntaxError: Invalid or unexpected token (Chrome)
Error type
What went wrong?
There is an invalid or unexpected token that doesn't belong at this position in the
code. Use an editor that supports syntax highlighting and carefully check your code
against mismatches like a minus sign (-) versus a dash (–)
or simple quotes (") versus non-standard quotation marks (").
Examples
Mismatched characters
Some characters look similar, but will cause the parser to fail interpreting your code. Famous examples of this are quotes, the minus or semicolon (greek question mark (U+37e) looks same).
“This looks like a string”; // SyntaxError: illegal character
// “ and ” are not " but look like it
42 – 13; // SyntaxError: illegal character
// – (en-dash) is not - but looks like it
const foo = "bar"; // SyntaxError: illegal character
// <37e> is not ; but looks like it
This should work:
"This is actually a string";
42 - 13;
const foo = "bar";
Some editors and IDEs will notify you or at least use a slightly different highlighting for it, but not all. When something like this happens to your code and you're not able to find the source of the problem, it's often best to just delete the problematic line and retype it.
Forgotten characters
It's easy to forget a character here or there.
const colors = ["#000", #333", "#666"];
// SyntaxError: illegal character
Add the missing quote for "#333".
const colors = ["#000", "#333", "#666"];
Hidden characters
When copy pasting code from external sources, there might be invalid characters. Watch out!
const foo = "bar";
// SyntaxError: illegal character
When inspecting this code in an editor like Vim, you can see that there is actually a zero-width space (ZWSP) (U+200B) character.
const foo = "bar";<200b>