How to make a input field readonly with JavaScript?

Question

You can get the input element and then set its readOnly property to true as follows:

document.getElementById('InputFieldID').readOnly = true;

Specifically, this is what you want:

<script type="text/javascript">
  function onLoadBody() {
    document.getElementById('control_EMAIL').readOnly = true;
  } 
</script>

Call this onLoadBody() function on body tag like:

<body onload="onLoadBody">

View Demo: jsfiddle.