Develop Reference

Starting from random pages in Google Web Designer

I've been using Google Web Designer for a few months and I have a question. I don't know if it's possible to do in GWD:
I want the index.html file to load a different random page, choosing between 3 pages. When you hit reload, it should load another random page, and so on. The pages don't need to appear in order. I'm trying to find out how this can be done but I had no success so far.

This can be accomplished with a custom JavaScript event handler.
The <gwd-doubleclick> element fires an adinitialized event before any content is displayed, which we can use to make sure our changes are applied before the user sees the first page. It also provides a .goToPage(n) method which we can use to switch pages. (goToPage has additional arguments that can be used to control animation between pages, but we can ignore those because we want the default behaviour of instantly jumping.)
Start by adding a new event handler.
target: document.body
event: Google Ad: Ad Initialized
action: Custom: Add Custom Action
configuration: a name of your choice (such as gwd.goToRandomPage), for the following code:
var pages = 3; // adjust as appropriate
var targetPage = Math.floor(Math.random() * pages);
event.target.goToPage(targetPage);
In code view you can see that this produces something like the following:
// This script block is auto-generated. Please do not edit!
gwd.actions.events.registerEventHandlers = function(event) {
gwd.actions.events.addHandler('document.body', 'adinitialized', gwd.goToRandomPage, false);
};
gwd.actions.events.deregisterEventHandlers = function(event) {
gwd.actions.events.removeHandler('document.body', 'adinitialized', gwd.goToRandomPage, false);
};
You could choose to skip the GWD UI and use the standard JavaScript event handling APIs to accomplish the same thing, with something along the lines of:
document.body.addEventListener('adinitialized', function() {
var pages = 3; // adjust as appropriate
var targetPage = Math.floor(Math.random() * pages);
event.target.goToPage(targetPage);
});
However, you probably want to avoid this in general, because it will prevent GWD from handling things like element renaming automatically.
If you'd like to jump to one of a specific set of pages, instead of selecting from all pages, you could use an array of page IDs instead.
var pageIds = ['page1_1', 'page1_2'];
var targetPage = pageIds[Math.floor(Math.random() * pageIds.length)];
event.target.goToPage(targetPage);
For future reference, you can find most of the component APIs described in the documentation. Questions about GWD that do not involve code or are otherwise unsuitable for Stack Overflow should be asked on the GWD support forum instead.

Click counter without javascript

I'm using this javascript for a click counter in my blogger blog:
function clickCounter() {
if(typeof(Storage) !== "undefined") {
if (sessionStorage.clickcount) {
sessionStorage.clickcount = Number(sessionStorage.clickcount)+1;
} else {
sessionStorage.clickcount = 1;
}
document.getElementById("result").innerHTML = "Correct! " + sessionStorage.clickcount + " Smart answers 'til now.";
} else {
document.getElementById("result").innerHTML = "Sorry, your browser does not support this quiz...";
}
}
<button onclick="clickCounter()" type="button">Suspension</button>
Is there any way to create something similar through a non javascript method?
Can you help me triger an event (extra text message through popup or within the page) every 5, 10, 20, 100 clicks?
Thank you very much

HTML, and the Web in general, was designed to be stateless.
When you pull up a page, it should be like the first time -- and every time -- you pull up the page.
Since then, people have come up with a number of techniques to add state -- to save data, but they all involved one of two methods -- or sometimes both.
Method 1: Store state on the server.
This method uses HTML forms or cookies to slip information to the server when you load and reload a page.
Method 2: Store state in the client
While there are some older versions of Internet Explorer that can be coded in VBA, we are going to ignore that. The only "real" way to run any kind of code on the client, to store any data, is to use JavaScript.
Method 3: Use the client to talk to the server
Using Ajax, you can let your client talk to the server, but without doing a page reload. This still uses JavaScript.
So, to answer your question:
Without a server
Without JavaScript
No, you cannot save or store anything.

I have not tried this but...
What if you put multiple buttons positioned on top of each other. As each one is clicked, it can be made to vanish with something like
a:visited { display: none; }
The ones that need to display a message (5th, 10th, etc.) have different behavior attached.
See on click hide this (button link) pure css

How to properly handle chrome extension updates from content scripts

In background page we're able to detect extension updates using chrome.runtime.onInstalled.addListener.
But after extension has been updated all content scripts can't connect to the background page. And we get an error: Error connecting to extension ....
It's possible to re-inject content scripts using chrome.tabs.executeScript... But what if we have a sensitive data that should be saved before an update and used after update? What could we do?
Also if we re-inject all content scripts we should properly tear down previous content scripts.
What is the proper way to handle extension updates from content scripts without losing the user data?

If you've established a communication through var port = chrome.runtime.connect(...) (as described on
https://developer.chrome.com/extensions/messaging#connect), it should be possible to listen to the runtime.Port.onDisconnect event:
tport.onDisconnect.addListener(function(msg) {...})
There you can react and, e.g. apply some sort of memoization, let's say via localStorage. But in general, I would suggest to keep content scripts as tiny as possible and perform all the data manipulations in the background, letting content only to collect/pass data and render some state, if needed.

Once Chrome extension update happens, the "orphaned" content script is cut off from the extension completely. The only way it can still communicate is through shared DOM. If you're talking about really sensitive data, this is not secure from the page. More on that later.
First off, you can delay an update. In your background script, add a handler for the chrome.runtime.onUpdateAvailable event. As long as the listener is there, you have a chance to do cleanup.
// Background script
chrome.runtime.onUpdateAvailable.addListener(function(details) {
// Do your work, call the callback when done
syncRemainingData(function() {
chrome.runtime.reload();
});
});
Second, suppose the worst happens and you are cut off. You can still communicate using DOM events:
// Content script
// Get ready for data
window.addEventListener("SendRemainingData", function(evt) {
processData(evt.detail);
}, false);
// Request data
var event = new CustomEvent("RequestRemainingData");
window.dispatchEvent(event);
// Be ready to send data if asked later
window.addEventListener("RequestRemainingData", function(evt) {
var event = new CustomEvent("SendRemainingData", {detail: data});
window.dispatchEvent(event);
}, false);
However, this communication channel is potentially eavesdropped on by the host page. And, as said previously, that eavesdropping is not something you can bypass.
Yet, you can have some out-of-band pre-shared data. Suppose that you generate a random key on first install and keep it in chrome.storage - this is not accessible by web pages by any means. Of course, once orphaned you can't read it, but you can at the moment of injection.
var PSK;
chrome.storage.local.get("preSharedKey", function(data) {
PSK = data.preSharedKey;
// ...
window.addEventListener("SendRemainingData", function(evt) {
processData(decrypt(evt.detail, PSK));
}, false);
// ...
window.addEventListener("RequestRemainingData", function(evt) {
var event = new CustomEvent("SendRemainingData", {detail: encrypt(data, PSK)});
window.dispatchEvent(event);
}, false);
});
This is of course proof-of-concept code. I doubt that you will need more than an onUpdateAvailable listener.

Getting Backbutton to work in single page website and implementing "speaking" URLs

I have a single page website and would like to achieve the following:
back button working as if it was a normal website
and instead of say,
www.mysite.com/index.php?p=#this-is-a-great-product
I'd like to have this url
www.mysite.com/this-is-a-great-product
while still having back button working properly.
Regarding 1.) I use the following code ive found which works great:
<!-- Getting BackButton to work properly -->
<script type="text/javascript">
var times = 0;
function doclick() {
times++;
}
function doclick() {
times++;
location.hash = times;
}
window.onhashchange = function() {
if (location.hash.length > 0) {
times = parseInt(location.hash.replace('#',''),10);
} else {
times = 0;
}
}
</script>
…but of course it just changes any anchors to /#1, then /#2 and so forth ro get the backbutton to work. But as I'm not a programmer I don't know how to change it… :(
Regarding 2.) i can add in htaccess this:
>RewriteEngine On
>RewriteRule ^([^/.]+)/?$ /index.php?page=$1
and this changes /index.php?p=products to /products.
So how do I change the above code (under 1.) so it doesn't change all anchors to #1, #2, etc. but instead references / uses the urls I achieved under 2, like
www.mysite.com/this-is-a-great-product
And (probably a very dumb question, but a very important one) -given I use only the new url links on my site- is there any danger that this still might result in duplicate content in any way?
Regarding this, should I (for that reason or any other) sefreferential my single page index.php to itself using rel canonical link=index.php?
Thanks so much in advance!

As mentioned, you will want to use the HTML5 History API. Please note, this API is relatively new and therefore browser support is a concern. At the time of writing, approximately 71% of global Internet users have support for it (see http://caniuse.com/#feat=history for browser support information). Therefore, you will want to ensure you have a fall-back solution for this. You will likely want to use the older #! solution that was popular before the HTML 5 History API was adopted.
If you use the history API to replace, for example, example.com/#!settings with example.com/settings and a user bookmarks that nicer URL, then when they go to visit it, their browser will make a request to the server for /settings (which doesn't actually exist in the web server's context). Therefore, you will need to make sure your web server has some redirection rules (i.e. RewriteEngine) such that it can take the pretty URLs and redirect them to the #! version (and then if the user's browser supports the history API it can replace that with the nice URL).
If you aren't very comfortable programming yourself, I'd recommend using a JavaScript library that does a lot of the work for you. I did some quick searching and discovered the following, though there might be better ones out there: https://github.com/browserstate/history.js

Basically i have created a small prototype on jsfiddle which tracks all the urls accessed via ajax calls.
Also contains navigation to access links back and forth .
How It Actually Works:
I have created a global array called history, which keeps track of all urls accessed via ajax in sequence.
also there a global index defined to keep track of the url being accessed when navigating back and forth the links in history array.
There is History section at the bottom of the jsfiddle, which shows the sequence in which the links are accessed by capturing the link names and posting them in the order in which they were accessed.
JS Code:
$(function () {
var history = [];
var index = 0;
$('.links').on('click', function () {
$('#history').append($(this).text());
var address = $(this).attr('data-ref');
index += 1;
history[index] = address;
$('.links').attr('disabled', 'disabled');
loadExternalPage(address);
console.log('list:' + history);
});
$('#back').on('click', function () {
console.log(index);
index -= 1;
console.log(index);
console.log(history[index]);
loadExternalPage(history[index]);
});
$('#forward').on('click', function () {
console.log(index);
index += 1;
console.log(index);
console.log(history[index]);
loadExternalPage(history[index]);
});
var loadExternalPage = function (address) {
console.log(history[index]);
$('#result-section').load(address, function () {
console.log('data-loaded');
$('.links').removeAttr('disabled');
});
};
});
Live Demo # JSFiddle:http://jsfiddle.net/dreamweiver/dpwmcu0b/8/
Note: This solution is far from being perfect, so dont consider it as final solution but rather use it as a base to build upon

On using BACK and FORWARD functions in the browser top-left button:
In principle, there is no great problem with this as long as you work with the existing storage object (a stack) for previously visited web pages on your browser. This object is the history object and you can see what is in it anytime by right-clicking and selecting "Inspect", then selecting the "Console" tab, then enter window.history and enter.
Check out the Browser Object Model (BOM) section of Pro Java For Web Developers (Frisbee) for the background to the history object. (Just a few pages, an easy read, don't worry.) Just remember that in this process you are storing the new page that you move to, not the old page that you are leaving !
For a simple SPA example, look at this example. codepen.io/tamjk/pen/NWxWOxL
In regard to the URL, the method that the history object uses to load a new page state into the history stack, i.e. pushState(...), has an optional third parameter for associating a dummy URL for each web page that is stored.
Personally, when I first sorted out the BACK & FORWARD functions, I did not use dummy URLs as the browser was being confused by them and I had enough to do sorting out the history sequence using just the first two parameters, i.e.
the state object - a JSON holding enough data to recreate the page stored
a title for the page I expect that you could also use a dummy URL but I will leave that to the student as an exercise, as they say.
But you can add the URL of the new page if you want to.
In the example above, for the state object I just used the IDs of the page's nav link and its content element.
For the title, I programmatically changed the HTML's page title element with each change of page. I did this after noticing that the browser listed the previous pages according to the title element in the HTML code.
Unfortunately, this title does not show up on CodePen when you right-click on the browser BACK and FORWARD buttons due to CodePen's system not allowing it. But it will show on your own sites.
It's important that whatever method you use to store current web page states when using the navbar links to navigate, you DO NOT ADD page states to the browser history when you arrive at them using BACK or FORWARD buttons. Otherwise your history stack will have repetitions of entries going back and deletion of entries going forward.
In the CodePen, this was achieved by having the addToHistory(..) function separate to and outside the scope of the switchPage(...) function. This allows you use of the switchPage function in both normal navbar navigation and browser BACK/FORWARD navigation. The third parameter of switchPage(...) is a boolean indicating if the page is to be stored in history or not.
Anyway, this is just something to get you started.

HTML5 → Dynamic associated Server Sent Events

I just started using SSE and wonder how I can make them more dynamic.
I'm using a Box to select users and an image and text changes corresponding to the username.
Now I want to check for user updates via SSE and want the user to be still selectable.
I tried to add the eventSource when I'm changing the <select> box:
function setSelected(elm) {
selectedName = elm.options[elm.selectedIndex].innerHTML;
var eSource = new EventSource("getState.php?passVar=" + selectedName);
eSource.onmessage = function(event) {
document.getElementById("stateText").innerHTML = event.data;
};
}
How can I reach my goal?
edit
I have now added the eventSource successfully (I had an issue with the source itself).
But when I now add another source, I have actually two sources running.
How can I remove the old one?

To remove the previous event source use the close() method. You're going to have to keep the reference to eSource around somehow to do this.