Change onClick attribute with javascript

The line onclick = writeLED(1,1) means that you want to immediately execute the function writeLED(arg1, arg2) with arguments 1, 1 and assign the return value; you need to instead create a function that will execute with those arguments and assign that. The topmost answer gave one example - another is to use the bind() function like so:

    var writeLEDWithSpecifiedArguments = writeLED.bind(this, 1,1);
    document.getElementById('buttonLED'+id).onclick = writeLEDWithSpecifiedArguments;

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);