Selecting all text in HTML text input when clicked

You can use the JavaScript .select() method for HTMLElement:

<label for="userid">User ID</label>
<input onClick="this.select();" value="Please enter the user ID" id="userid" />

But apparently it doesn’t work on mobile Safari. In those cases you can use:

<input onClick="this.setSelectionRange(0, this.value.length)" value="Sample Text" id="userid" />