Edit in JSFiddle

<span id="foo">Foo </span><br/>
Enter value for Foo : <input id="fooVal"><br/><br/>

<button id="addVal">Add Foo value </button> 
<button id="showVal">Show Foo value </button>

$(function() {
    // adding value 1 to key bar  
    $("#foo").data("bar", "1");
});

$("#addVal").click(function() {
    var value = $("#fooVal").val();
    // Update value assigned to key bar   
    $("#foo").data("bar", value);
    alert("value updated!");
});

$("#showVal").click(function() {
    // retrieve value assigned to key bar
    alert($("#foo").data("bar"));
});