html - Change 2 strings on load with javascript -

i try replace 2 parts of string in lot of pages on page load.

in case, replace:

<iframe width="890" height="514" src="https://www.youtube.com/embed/ 

with string and

?enablejsapi=1" frameborder="0" allowfullscreen="allowfullscreen"></iframe> 

with one. tried use

<script type="text/javascript"> window.onload = clear; function clear() { document.body.innerhtml = document.body.innerhtml.replace(/xxx/g, 'yyy'); } </script>     

but did not work.

it needs done on page load. idea? thank you!

edit:

what try do, split youtube embed in div. part before unique youtube id needs replaced , part after id needs replaced. complete link like:

<iframe width="890" height="514" src="https://www.youtube.com/embed/xxxxxxxx?enablejsapi=1" frameborder="0" allowfullscreen="allowfullscreen"></iframe> 

the part before xxxxxxxx , part after xxxxxxxx need changed on load more complete code including div's , classes.

thank you!