HTML how to clear input using javascript?

<script type="text/javascript">
    function clearThis(target) {
        if (target.value == '[email protected]') {
            target.value = "";
        }
    }
</script>

Is this really what your looking for?

you can use attribute placeholder

<input type="text" name="email" placeholder="[email protected]" size="30" />

or try this for older browsers

<input type="text" name="email" value="[email protected]" size="30" onblur="if(this.value==''){this.value='[email protected]';}" onfocus="if(this.value=='[email protected]'){this.value='';}">

For me this is the best way:

<form id="myForm">
  First name: <input type="text" name="fname" value="Demo"><br>
  Last name: <input type="text" name="lname"><br><br>
  <input type="button" onclick="myFunction()" value="Reset form">
</form>
     
<script>
function myFunction() {
    document.getElementById("myForm").reset();
}
</script>