You have to use negative index in String.prototype.slice() function.

• using negative index as first argument
  returns the sliced string to the 6 elements counting from the end of the string.

var example = javascript;

console.log(example.slice(-6)); 

• using negative index as the second argument returns the sliced
  string from 0 to the 6th element counting from the end. It's opposite to the first method.

var example = javascript;



console.log(example.slice(0, -6));

In your particular case, you have to use the second method.

console.log('11001000000000000001010'.slice(0, -18));



console.log('110000000001101011100'.slice(0, -18));

If you want to read more about that function, visit: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice