/*
 * Schedule an invocation or invocations of f() in the future.
 * Wait start milliseconds, then call f() every interval milliseconds,
 * stopping after a total of start+end milliseconds.
 * If interval is specified but end is omitted, then never stop invoking f.
 * If interval and end are omitted, then just invoke f once after start ms.
 * If only f is specified, behave as if start was 0.
 * Note that the call to invoke() does not block: it returns right away.
 */
function invoke(f, start, interval, end) {
    if (!start) start = 0; // Default to 0 ms
    if (arguments.length <= 2) // Single-invocation case
        setTimeout(f, start); // Single invocation after start ms.
    else { // Multiple invocation case
        setTimeout(repeat, start); // Repetitions begin in start ms
        function repeat() { // Invoked by the timeout above
            var h = setInterval(f, interval); // Invoke f every interval ms.
            // And stop invoking after end ms, if end is defined
            if (end) setTimeout(function() {
                clearInterval(h);
            }, end);
        }
    }
}

/*
 * This function parses ampersand-separated name=value argument pairs from
 * the query string of the URL. It stores the name=value pairs in
 * properties of an object and returns that object. Use it like this:
 *
 * var args = urlArgs(); // Parse args from URL
 * var q = args.q || ""; // Use argument, if defined, or a default value
 * var n = args.n ? parseInt(args.n) : 10;
 */
function urlArgs() {
    var args = {}; // Start with an empty object
    var query = location.search.substring(1); // Get query string, minus '?'
    var pairs = query.split("&"); // Split at ampersands
    for (var i = 0; i < pairs.length; i++) { // For each fragment
        var pos = pairs[i].indexOf('='); // Look for "name=value"
        if (pos == -1) continue; // If not found, skip it
        var name = pairs[i].substring(0, pos); // Extract the name
        var value = pairs[i].substring(pos + 1); // Extract the value
        value = decodeURIComponent(value); // Decode the value
        args[name] = value; // Store as a property
    }
    return args; // Return the parsed arguments
}

location = "http://www.oreilly.com"; // Go buy some books!
location = "page2.html"; // Load the next page
/**
 * #top不存在时，浏览器跳到文档开始处
 */
location = "#top"; // Jump to the top of the document
location.search = "?page=" + (pagenum+1); // load the next page

history.back();
history.forward();
history.go(0);
history.go(-2);