# SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'

The JavaScript exception "unparenthesized unary expression can't appear on the left-hand side of '**'" occurs when a unary operator (one of `typeof`, `void`, `delete`, `await`, `!`, `~`, `+`, `-`) is used on the left operand of the exponentiation operator without parentheses.

## Message

```SyntaxError: Unary operator used immediately before exponentiation expression. Parenthesis must be used to disambiguate operator precedence (V8-based)
SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**' (Firefox)
SyntaxError: Unexpected token '**'. Ambiguous unary expression in the left hand side of the exponentiation expression; parentheses must be used to disambiguate the expression. (Safari)
```

## What went wrong?

You likely wrote something like this:

``````-a ** b
``````

Whether it should be evaluated as `(-a) ** b` or `-(a ** b)` is ambiguous. In mathematics, -x2 means `-(x ** 2)` — and that's how many languages, including Python, Haskell, and PHP, handle it. But making the unary minus operator take precedence over `**` breaks symmetry with `a ** -b`, which is unambiguously `a ** (-b)`. Therefore, the language forbids this syntax and requires you to parenthesize either side to resolve the ambiguity.

``````(-a) ** b
-(a ** b)
``````

Other unary operators cannot be the left-hand side of exponentiation either.

``````await a ** b
!a ** b
+a ** b
~a ** b
``````

## Examples

When writing complex math expressions involving exponentiation, you may write something like this:

``````function taylorSin(x) {
return (n) => (-1 ** n * x ** (2 * n + 1)) / factorial(2 * n + 1);
// SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'
}
``````

However, the `-1 ** n` part is illegal in JavaScript. Instead, parenthesize the left operand:

``````function taylorSin(x) {
return (n) => ((-1) ** n * x ** (2 * n + 1)) / factorial(2 * n + 1);
}
``````

This also makes the code's intent much clearer to other readers.