javascript return highest

function returnhighest(input) {
var donothing = 0
var temp = 0
var highest = 0
for (var i=0;i < idtotalarray.length;i++) { input == idrarray[i] ? temp=idtotalarray[i] : donothing=donothing 
                                        temp > highest ? highest=temp : donothing=donothing }       
return highest      
}