Isograms.js

/**
 * Check to see if a string has repeating letters.
 */
function isIsogram(str) {
    var i, j;
    str = str.toLowerCase();
    for(i = 0; i < str.length; ++i)
      for(j = i + 1; j < str.length; ++j)
        if(str[i] === str[j])
          return false;
    return true;
}

console.log(isIsogram("Here I am."))