Pre process pattern string for KMP algorithm

KMP preprocess pattern.js

function preProcess(pattern) {
  let lps = new Array(pattern.length);
  let i = 0, j = 1; lps[0] = 0;
  while (j < pattern.length) {
	if(pattern[j] == pattern[i]) {
		lps[j] = i + 1;
  		i++;
          	j++;
      	  } else if(i != 0) {
		i = lps[i-1];
	  } else {
		lps[j] = 0;
		j++;
	  }
  }
  return lps;
}