Author: John Au-Yeung

Sometimes, we may run into the ‘SyntaxError: missing ) after condition’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: missing ) after condition’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: missing ) after condition’ When Developing JavaScript Apps

To fix the ‘SyntaxError: missing ) after condition’ when we’re developing JavaScript apps, we should make sure we have a closing parentheses for each opening parentheses in the head of our if statements.

On Edge, the error message for this error is SyntaxError: Expected ')'.

On Firefox, the error message for this error is SyntaxError: missing ) after condition.

For instance, if we have code like:

if (3 > Math.PI {
  console.log("error");
}

then we should get error since the head of the if statement is missing the closing parentheses.

To fix this, we write:

if (3 > Math.PI) {
  console.log("error");
}

We also can’t use the is operator for comparison in JavaScript since it doesn’t exist in JavaScript, so instead of writing:

if (done is true) {
 console.log("we are done");
}

which will throw the error, we write:

if (done === true) {
 console.log("we are done");
}

to use the === operator to comparison done to true.

Conclusion

To fix the ‘SyntaxError: missing ) after condition’ when we’re developing JavaScript apps, we should make sure we have a closing parentheses for each opening parentheses in the head of our if statements.

On Edge, the error message for this error is SyntaxError: Expected ')'.

On Firefox, the error message for this error is SyntaxError: missing ) after condition.

Sometimes, we may run into the ‘SyntaxError: missing ) after argument list’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: missing ) after argument list’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: missing ) after argument list’ When Developing JavaScript Apps

To fix the ‘SyntaxError: missing ) after argument list’ when we’re developing JavaScript apps, we should make sure we have corresponding closing parentheses for each opening parentheses in our JavaScript code.

On Edge, the error message for this error is SyntaxError: Expected ')'.

And on Firefox, the error message for this error is SyntaxError: missing ) after argument list.

For instance, if we write:

console.log('PI: ' Math.PI);

then the error will be thrown because we’re missing the comma between 'PI: ' and Math.PI.

To fix this, we write:

console.log('PI: ',  Math.PI);

The error will also be thrown if we have unterminated strings.

For instance, if we write:

console.log('"Java"' + 'Java' + 'Script\");

then we’ll get the error since we don’t have a closing single quote in the 'Script\" string.

To fix this, we write:

console.log('"Java"' + 'Java' + 'Script\"');

Conclusion

To fix the ‘SyntaxError: missing ) after argument list’ when we’re developing JavaScript apps, we should make sure we have corresponding closing parentheses for each opening parentheses in our JavaScript code.

On Edge, the error message for this error is SyntaxError: Expected ')'.

And on Firefox, the error message for this error is SyntaxError: missing ) after argument list.

Sometimes, we may run into the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: invalid regular expression flag "x"’ When Developing JavaScript Apps

To fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps, we should make sure that we add flags to our JavaScript regex that’s accepted by the JavaScript engine.

On Edge, the error message for this error is SyntaxError: Syntax error in regular expression.

On Firefox, the error message for this error is SyntaxError: invalid regular expression flag "x".

And on Chrome, the error message for this error is SyntaxError: Invalid regular expression flags.

The general format for a JavaScript to declare a JavaScript regex is:

const re = /pattern/flags;

We can also use the RegExp constructor to declare a regex:

const re = new RegExp('pattern', 'flags');

The following flags are valid JavaScript regex flags:

• g Global search.
• i Case-insensitive search.
• m Multi-line search.
• s Allow . to match newlines (added in ES2018)
• u Unicode; treat pattern as a sequence of Unicode code points
• y Perform a "sticky" search that matches starting at the current position in the target string.

Therefore, we shouldn’t write code like:

/foo/bar;

since bar isn’t a valid JavaScript regex flag.

Instead, we write:

/foo/g;

which has the g flag, which is a valid flag.

Conclusion

To fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps, we should make sure that we add flags to our JavaScript regex that’s accepted by the JavaScript engine.

On Edge, the error message for this error is SyntaxError: Syntax error in regular expression.

On Firefox, the error message for this error is SyntaxError: invalid regular expression flag "x".

And on Chrome, the error message for this error is SyntaxError: Invalid regular expression flags.

Sometimes, we may run into the ‘SyntaxError: illegal character’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: illegal character’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: illegal character’ When Developing JavaScript Apps

To fix the ‘SyntaxError: illegal character’ when we’re developing JavaScript apps, we should make sure we didn’t have any characters that the JavaScript doesn’t accept in out code.

On Edge, the error message for this error is SyntaxError: Invalid character.

On Firefox, the error message for this error is SyntaxError: illegal character.

And on Chrome, the error message for this error is SyntaxError: Invalid or unexpected token.

For instance, the following code will throw the error:

“This looks like a string”;
2 – 13; 
let foo = 'bar';

In the first line, the “ and ” characters aren’t the same as the double quote characters accepted by JavaScript engines, which is ".

In the 2nd line, – isn’t the same as the minus sign, which is -.

And in the last line, ; is the <37e> character, which isn’t the same as the semicolon accepted by JavaScript.

To fix this, we write:

"This is a string";
42 - 13;
let foo = 'bar';

This error is also thrown when we forgot some character.

For instance, the error will be thrown when we write:

const colors = ['#000', white', '#666'];

We forgot the opening single quote in the 2nd string.

To fix this, we write:

const colors = ['#000', 'white', '#666'];

We should also remove hidden characters that may cause this error,

For instance, the following code:

const foo = 'bar';

has a zero-width space at the end. Once we remove it, then the code runs.

Conclusion

To fix the ‘SyntaxError: illegal character’ when we’re developing JavaScript apps, we should make sure we didn’t have any characters that the JavaScript doesn’t accept in out code.

On Edge, the error message for this error is SyntaxError: Invalid character.

On Firefox, the error message for this error is SyntaxError: illegal character.

And on Chrome, the error message for this error is SyntaxError: Invalid or unexpected token.

Sometimes, we may run into the ‘SyntaxError: identifier starts immediately after numeric literal’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: identifier starts immediately after numeric literal’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: identifier starts immediately after numeric literal’ When Developing JavaScript Apps

To fix the ‘SyntaxError: identifier starts immediately after numeric literal’ when we’re developing JavaScript apps, we should make sure we don’t declare on reference variable names that starts with numeric literals.

For instance, the following code will all throw the error:

const 1bar = 'foo';
const foo = 1bar;
console.log(1.foo);

Instead, we write:

const bar1 = 'foo';
const foo = bar1;

which don’t start with a numeric literal.

Conclusion

To fix the ‘SyntaxError: identifier starts immediately after numeric literal’ when we’re developing JavaScript apps, we should make sure we don’t declare on reference variable names that starts with numeric literals.