javascript - Elegant method to compare an array of strings to another array of strings -

question: how can elegantly compare array of strings array of strings returning array of non-matching strings

var master = ['1','2','3','4'] var versioned = ['1a','2','3b','4'] var errorlog = [] var count = 0; //this loop doesn't work :( for(var = 0; < versioned.length - 1; ++i ){     for(var j = 0; j < master.length -1; ++j){         if(versioned[i] === master[j]){             console.log('cleared');         }         if(count === master.length){             errorlog.push(versioned[i]);         }     } } 

loop return ['1a', '3b'];

i feel filter() or map() or reduce() i'm unable wrap brain around properly.

var master = ['1','2','3','4']; var versioned = ['1a','2','3b','4'];  function diff(needle, haystack){   return needle.filter(function(item){     return !~haystack.indexof(item);    }); }  console.log(diff(versioned, master)); //["1a", "3b"]; 

~ noting number equals -(x + 1). ~-1 becomes 0, falsy.

~master.indexof(item) same master.indexof(item) !== -1