Check out example codes for "html input default value". It will help you in understanding the concepts better.

Code Example 1

<input value="someStandardValue"/>

Code Example 2

<input id = idhere type = text placeholder = 'default value'>

Code Example 3

<form 
    action="/action_page.php">

  <label for="fname">First name:</label>
  <input type="text" id="fname" 
    name="fname" value="John"><br><br>
  <label for="lname">Last 
    name:</label>
  <input type="text" id="lname" name="lname" 
    value="Doe"><br><br>
  <input type="submit" value="Submit">

    </form>

Code Example 4

<input type="text" id="fname" name="fname" value="John">

Code Example 5

document.getElementById("myHiddenInputID").value = "MyNewValue";

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