match regex - How to get the difference between the two strings when matched

Question

I perform a test if a string contains a substring, if yes, I would like to have the substring that not matched

var string = "Hello world";
var toMatch = new RegExp('world', 'i');

if (string.match(toMatch)){
  // should return "Hello "
}

Answer 1

Just use replace() :

var string = "Hello world";
var toMatch = new RegExp('world', 'i');

var newString=string.replace(string.match(toMatch),"");

If you want to return, use

return string.replace(string.match(toMatch),"");

It will give you a string without "world" if it contained "world" and unmodified string if there was no "world"