I am new to Javascript. I want to write a javascript code that when I click a button, the alert window pops up and writes data-message attribute. Here is my code:

<button type=button data-message=a1 onclick=pop()>click</button>



<script>

  function pop() {

    alert(this.getAttribute(data-message));

  }

</script>

but I get the error

TypeError: this.getAttribute is not a function

alert(this.getAttribute(data-message));

I have two questions:

1. What is wrong?




2. How can I debug this? How can I find out what this refers to? I am using firebug.

Thanks a lot.