shultz,
а так?
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
window.addEventListener('DOMContentLoaded', function() {
function change () {
this.value.indexOf(this.defaultValue) && (this.value = this.defaultValue);
}
[].forEach.call(document.querySelectorAll('.user_linkedin_1'), function(item) {
item.addEventListener('input', change, false);
});
});
</script>
</head>
<body>
<input type="text" value="http://youtube.com/" style="width: 500px;" class="user_linkedin_1"><br>
<input type="text" value="http://www.yandex.ru/" style="width: 500px;" class="user_linkedin_1">
</body>
</html>