html value attribute
<!-- The value attribute is used to for example fill data to an input -->
<input type="text" value="I was already filled" id="textInput">
<!-- The value can be set or copied using JavaScrpit -->
<script>
// Get your element
var input = document.getElementById('textInput');
// get the value
var value = input.value;
// set the value
input.value = "i was changed";
</script>