how to get empty input field when click option in javascript code example

Example: empty a select input using js

// Fast javascript function to clear all the options in an HTML select element
// Provide the id of the select element
// References to the old <select> object will become invalidated!
// This function returns a reference to the new select object.
function ClearOptionsFast(id)
{
	var selectObj = document.getElementById(id);
	var selectParentNode = selectObj.parentNode;
	var newSelectObj = selectObj.cloneNode(false); // Make a shallow copy
	selectParentNode.replaceChild(newSelectObj, selectObj);
	return newSelectObj;
}

// This is an alternative, simpler method.  Thanks to Victor T.
// It does not appear to be as fast as the ClearOptionsFast method in FF 3.6.
function ClearOptionsFastAlt(id)
{
	document.getElementById(id).innerHTML = "";
}