Js determines whether the user has entered the correct image address

<Script language = "javascript">
<! --
Function putpic ()
{
Var picurl = window. prompt ("Enter the complete path of the image:", "http ://");
If (picurl! = Null)
{
If (picurl. length <16 | picurl. indexOf (". ") <7 | (picurl. indexOf (". gif ") <7 & picurl. indexOf (". GIF ") <7 & picurl. indexOf (". jpg ") <7 & picurl. indexOf (". JPG ") <7 & picurl. indexOf (". swf ") <7 & picurl. indexOf (". SWF ") <7 ))
{
Alert ("the post path is incorrect. Please check carefully! "+ Picurl. indexOf (". gif "));
}
Else
{
Document. forms [0]. putwords_temp.value = document. forms [0]. putwords_temp.value + "[img]" + picurl + "[/img]";
}
}
}
Function putlink ()
{
Var linkurl = window. prompt ("Enter the hyperlink address:", "http ://");
If (linkurl! = Null & linkurl! = "Http ://")
{
Document. forms [0]. putwords_temp.value = document. forms [0]. putwords_temp.value + "[url]" + linkurl + "[/url]";
}
}