Question

function myFunction(par) {
...
}


el1.onclick=myFunction(5);
el2.onclick=myFunction(7);

How to get a reference for the caller element inside myFunction?

Answer 1

//this is saying call this function and asign what it returns to onclick
el1.onclick= myFunction(5);

You want to use a closure
el1.onclick = function(){myFunction(5);}

To reference the element you can pass the object in

function test(elem, x){    
    elem.innerHTML = x;
} 

document.getElementById("foo").onclick = function(){ test(this, 1); }

example 1

or you can use call so that within the listener, this references the element.

function test(x){    
    this.innerHTML = x;
}

document.getElementById("foo").onclick = function(){ test.call(this, 1); }

example 2