JavaScript string converted to function eval ("string")

JavaScript has a very useful function of eval ("string")
This function can convert a string into an object or a statement that can be executed, such as your code can be used
Obj2=eval ("DOCUMENT.A.C" +i), in addition you can also write eval ("alert ()"),
Eval ("a+=2") so that you can let the user input the JavaScript statement execute
Your Docheck () can be changed as follows:
function Docheck () {
Obj1=eval ("DOCUMENT.A.A" +i)
Obj2=eval ("DOCUMENT.A.C" +i)
Obj1.value=obj2.options[obj2.selectedindex].value;
}

JavaScript string converted to function eval ("string")