Compare onclick action of two html button using javascript

I have this two HTML Form buttons with an onclick action associated t开发者_JAVA百科o each one.

<input type=button name=sel value="Select all" onclick="alert('Error!');">
<input type=button  name=desel value="Deselect all" onclick="alert('Error!');">

Unfortunately this action changes from time to time. It can be

onclick="";>

or

onclick="alert('Error!');"

or

onclick="checkAll('stato_nave');"  

I'm trying to write some javascript code that verifies what is the function invoked and change it if needed:

var button=document.getElementsByName('sel')[0];
// I don't want to change it when it is empty or calls the 'checkAll' function
if( button.getAttribute("onclick") != "checkAll('stato_nave');" &&
    button.getAttribute("onclick") != ""){
    //modify button
    document.getElementsByName('sel')[0].setAttribute("onclick","set(1)");
    document.getElementsByName('desel')[0].setAttribute("onclick","set(0)");
} //set(1) and set(0) being two irrelevant function

Unfortunately none of this work. Going back some steps I noticed that

alert( document.getElementsByName('sel')[0].onclick);

does not output the onclick content, as I expected, but outputs:

function onclick(event) {
    alert("Error!");
}

So i guess that the comparisons fails for this reason, I cannot compare a function with a string.

Does anyone has a guess on how to distinguish which function is associated to the onclick attribute?

---

This works

http://jsfiddle.net/mplungjan/HzvEh/

var button=document.getElementsByName('desel')[0];
// I don't want to change it when it is empty or calls the 'checkAll' function
var click = button.getAttribute("onclick");
if (click.indexOf('error') ) {

    document.getElementsByName('sel')[0].onclick=function() {setIt(1)};
    document.getElementsByName('desel')[0].onclick=function() {setIt(0)};

}

function setIt(num) { alert(num)}

But why not move the onclick to a script

window.onload=function() {
  var button1 = document.getElementsByName('sel')[0];
  var button2 = document.getElementsByName('desel')[0];
  if (somereason && someotherreason) {
    button1.onclick=function() {
      sel(1);
    }
    button2.onclick=function() {
      sel(0);
    }
  }
  else if (somereason) {
    button1.onclick=function() {
      alert("Error");
    }
  }
  else if (someotherreason) {
    button1.onclick=function() {
      checkAll('stato_nave')
    }
  }
}

---

Try casting the onclick attribute to a string. Then you can at least check the index of checkAll and whether it is empty. After that you can bind those input elements to the new onclick functions easily.

---

var sel = document.getElementsByName('sel')[0];
var desel = document.getElementsByName('desel')[0];

var onclick = sel.getAttribute("onclick").toString();

if (onclick.indexOf("checkAll") == -1 && onclick != "") {
    sel.onclick = function() { set(1) };
    desel.onclick = function() { set(0) };
}

function set(number)
{
    alert("worked! : " + number);
}

---

working example: http://jsfiddle.net/fAJ6v/1/

---

working example when there is a checkAll method: http://jsfiddle.net/fAJ6v/3/