Vanilla JavaScript version of jQuery .click

So maybe I'm just not looking in the right places but I can't find a good explanation of how to do the equivalent of jQuery's

$('a').click(function(){
    // code here
});

in plain old JavaScript?

Basically I want to run a function every time an a tag is clicked but I don't have the ability to load jQuery into the page to do it in the way above so I need to know how to do it using plain JavaScript.