Edit on Load event

I want to add this to EditOnLoad event. I need a proper syntax. Can someone help?

{literal}

<script language="JavaScript" type="text/javascript">

document.forms.editform.value_Status.onchange=function()

{

if(this.options[this.selectedIndex].value=='Completed')

document.forms.editform.value_ProjectName.disabled=true;

else

{

document.forms.editform.value_ProjectName.disabled=false;
}

}

</script>

{/literal}