Develop a JavaScript function that takes a string as input and returns a new string with all vowels removed.
Here's a JavaScript function that removes all vowels from the input string:

```javascript
function removeVowels(str) {
  return str.replace(/[aeiou]/gi, '');
}

// Example usage:
console.log(removeVowels("Hello World")); // Output: "Hll Wrld"
```

This function uses the `replace` method of the string object to replace all occurrences of vowels (both uppercase and lowercase) with an empty string. The regular expression `/[aeiou]/gi` is used to match any vowel character in the input string.