html - Change onClick attribute with javascript

Question

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;
    }
}

Answer 1

Well, just do this and your problem is solved :

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

Have a nice day XD