My solution to set a local cache with expiration, using HTML5 LocalStorage. This dramatically increases the performance of a mobile application.

LocalStorageExpires.js

/* Author: Brynner Ferreira (brynner.net) */
// Functions
function removeHtmlStorage(name) {
    localStorage.removeItem(name);
    localStorage.removeItem(name+'_time');
}
function setHtmlStorage(name, value, expires) {
    if (expires==undefined || expires=='null') { var expires = 3600; } // default: 1h
    var date = new Date();
    var schedule = Math.round((date.setSeconds(date.getSeconds()+expires))/1000);
    localStorage.setItem(name, value);
    localStorage.setItem(name+'_time', schedule);
}
function statusHtmlStorage(name) {
    var date = new Date();
    var current = Math.round(+date/1000);
    // Get Schedule
    var stored_time = localStorage.getItem(name+'_time');
    if (stored_time==undefined || stored_time=='null') { var stored_time = 0; }
    // Expired
    if (stored_time < current) {
        // Remove
        removeHtmlStorage(name);
        return 0;
    } else {
        return 1;
    }
}
// Status
var cache_status = statusHtmlStorage('cache_name');
// Has Data
if (cache_status == 1) {
    // Get Cache
    var data = localStorage.getItem('cache_name');
    alert(data);
// Expired or Empty Cache
} else {
    // Get Data
    var data = 'Pay in cash :)';
    alert(data);
    // Set Cache (30 seconds)
    if (cache) { setHtmlStorage('cache_name', data, 30); }
}