javascript - How to select all <a> tag and register onclick event?

Question

I am trying to select all the <a> tags in the page and register onclick even to them.

My codes:

document.getElementsByTagName('a').onclick = show;


var show = function(){
    alert('hahahha');
}

It doesn't work and my brain is fry now. Any ideas? Thanks a lot.

Answer 1

You're setting the onclick attribute to the array of elements, not to each element individually like you need. Also, you're defining show after you've used it.

var elts = document.getElementsByTagName('a');
var show = function() { alert('hahahha'); }
for (var i = elts.length - 1; i >= 0; --i) {
    elts[i].onclick = show;
}

It's more efficient to iterate backwards through the array than to test elts.length each time through. If you need to iterate forward, store the array length in a variable for better efficiency.