Change onClick attribute with javascript

This is my function and it should change the onClick attribute of the HTML input, but if I use

document.getElementById('buttonLED'+id).onclick = "writeLED(1,1)";

it does not work at all, but if I use

document.getElementById('buttonLED'+id).onclick = writeLED(1,1);

the function executes by itself! Any ideas what code do I have to use to change the onCLick attribute WITHOUT executing the function, before the button is clicked?
Here is the full function, if it matters:

function showLED(id){
    if(color == 0){
        document.getElementById('buttonLED'+id).onclick = "writeLED(1,1)";
        document.getElementById('buttonLED'+id).value="light is on";
        //document.getElementById('buttonLED'+id).disabled = false;
    }else{
        document.getElementById('buttonLED'+id).onclick = "writeLED(1,0)";
        document.getElementById('buttonLED'+id).value="light is off";
        //document.getElementById('buttonLED'+id).disabled = false;
    }
}

Well, just do this and your problem is solved :

document.getElementById('buttonLED'+id).setAttribute('onclick','writeLED(1,1)')

Have a nice day XD

You want to do this - set a function that will be executed to respond to the onclick event:

document.getElementById('buttonLED'+id).onclick = function(){ writeLED(1,1); } ;

The things you are doing don't work because:

1. The onclick event handler expects to have a function, here you are assigning a string

   document.getElementById('buttonLED'+id).onclick = "writeLED(1,1)";
   

2. In this, you are assigning as the onclick event handler the result of executing the writeLED(1,1) function:

   document.getElementById('buttonLED'+id).onclick = writeLED(1,1);