javascript createElement通过appendChild返回错误

Question

I'm trying to write a short javascript function to add buttons for prev/next to a css-slider I've put together.
I don't have access to the DOM, so figured I'd just insert the div's via javascript. Here is the function:

function createfn(){
  var element = document.createElement("div");
  var prev = document.createTextNode("<");
  element.appendChild(prev);
  document.getElementsByClassName("sqs-gallery")[0].appendChild(element);
}
window.onload=createfn();

I am getting an error:

"Cannot read property 'appendChild' of undefined"

The div container with class .sqs-gallery is definitely appearing on the page. I was questioning whether this was somehow running before the DOM fully loaded, but I have the window.onload in there which (I believe) should wait until everything is loaded before running the function.

Any and all thoughts and help is greatly appreciated!

Answer 1

You perform window.onload=createfn() ;

it means that you assign result of createfn() to onload (not the function). And function " createfn " being executed immediately (does not wait for window loading).

Just remove parentheses to assign handler instead of function value.

Answer 2

If you leave the code as window.onload=createfn() (with the parenteheses) createfn will run directly as the code starts to run (even before the DOM has loaded) because the result needs to be assigned to window.onload .

What you instead should be trying to do is assign the function, not the result: window.onload=createfn . This should work just fine.