var dotUElements = document.getElementsByClassName("u");

for (var ii = 0; ii < dotUElements.length; ii++) {
    dotUElements[ii].onmouseover = createHandler1( dotUElements[ii] );
    dotUElements[ii].onmouseout = createHandler2( dotUElements[ii] );
}

function createHandler1( myobj ) {
    return (function() {ff1(myobj);});
}

function createHandler2( myobj ) {
    return (function() {ff2(myobj);});
}

function ff1 (myobj) {
    myobj.style.color="red";
    var uChar = myobj.firstChild.nodeValue;
    var uNum =  uChar.charCodeAt(0);
    uName = unicodeTable(uNum);
    var uHex = (uNum).toSring(16);
}

function ff2 (myobj) {
    myobj.style.color="black";
}

var uHex = (uNum).toSring(16);

Error: TypeError: uNum.toSring is not a function

(30).toSring(16);