Question

I’m trying to execute JavaScript functions that are called when a event (for example onClick event) is performed on a web page with JavaScript code. I’m getting the function from the event like this :

var attributval = document.getElementsByTagName("a").getAttribute('onClick');

and I’m trying to execute this object (which a JavaScript function in fact) as a function (suppose we have <a onClick = alert('whatever');> on this example, I tried:

var attributval = document.getElementsByTagName("a").getAttribute('onClick');
attributval() = function(){attributval};
attributval();

but it didn’t work.

Answer 1

A DOM attribute is not the same as a JavaScript property (even though they can have the same name onclick). You should use

var attributval = document.getElementsByTagName("a")[0].onclick;

to retrieve a function (or null) from the JS object (as opposed to getAttribute(), which will most likely return a toString() for the property).

Now, attributval() = is illegal syntax, as attributval() is not an l-value (you cannot assign to it).

attributval(); will work but without the second line (which is illegal JavaScript) it will invoke the original A element onclick handler (if one is defined) or throw an exception (if the onclick handler is null).