Set the value of an input field

if your form contains an input field like

<input type='text' id='id1' />

then you can write the code in javascript as given below to set its value as

document.getElementById('id1').value='text to be displayed' ; 

I use 'setAttribute' function:

<input type="text" id="example"> // Setup text field 
<script type="text/javascript"> 
  document.getElementById("example").setAttribute('value','My default value');
</script>

This is one way of doing it:

document.getElementById("nameofid").value = "My value";