Edit in JSFiddle

var input = document.getElementById('input');
var save = document.getElementById('save');

save.addEventListener('click', function() {
    localStorage.setItem("item", input.value);
    document.getElementById('output').innerHTML = "SAVED";
});

<input type="text" id="input"></input><br/>
<button id="save">Save</button>
<br/><br/>
Result: <span id="output"></span>
 

span {
    color: #f00;
}