Javascript verifies that the URL address entered by the user is null and properly formatted

<script type="text/javascript">

function checkUrl() {

var url = document.getElementById('url').value;

if (url==''){

alert('URL  The address cannot be empty ');

return false;

} else if (!isURL(url)) {

alert('URL  The format should be  //www.jb51.net');

return false;

} else {

return true;

}

return false;

}
function isURL(str)

{

//varreg=/[0-9a-zA-z]+.(html|htm|shtml|jsp|asp|php|com|cn|net|com.cn|org)$/;

//Must contain.(last one. At least one character in front) and. At least one word character in the back. The last character must be a word character or /

varreg=/w+.(w+|w+/)$/;

varisurl=reg.test(str);//The test(STR) method is an object built into the correct js expression that can be called 
 directly
returnisurl;

}

</script>

<form action="" method="post" onsubmit="checkUrl();">
URL:

<input type="text" name="url" id="url" value="//www.jb51.net" onfocus="this.value=''"/>

<br /><br />

<input type="submit" value=" Get the address " name="get"/>

<input type="submit" value=" download " name="download"/>

</form>

PHP detects the validity of the URL address

The following code

<?

function is_url($str){

return preg_match("/^http://[A-Za-z0-9]+.[A-Za-z0-9]+[/=?%-&_~`@[]':+!]*([^<>"])*$/", $str);

}

?>

If we want to see if we can do this properly we can use the file_get_contents() function to verify.