String.prototype.leftPad = function (l, c) { return new Array(l - this.length + 1).join(c || '0') + this; }

function utf8ToUnicode(s){var r = []; for(var i=0, len=s.length; i<len; i++) r.push("\\u"+s.charCodeAt(i).toString(16).leftPad(4)); return r.join(''); }

console.log(utf8ToUnicode('سلام'));