unkind,
<html>
<head>
<title>Обмен переменных</title>
<meta charset="utf-8">
<script>
window.addEventListener('DOMContentLoaded', function() {
var nodes = document.querySelectorAll('#x,#y');
[].forEach.call(nodes, function(item, i) {
item.addEventListener('blur', function() {
var val = this.value;
item.value = nodes[+!i].value
nodes[+!i].value = val;
});
}); });
</script>
</head>
<body>
<input type="text" id="x" >
<input type="text" id="y" >
</body>
</html>