Sunday, June 24, 2018

Updates and missing sidebar stuff...

Just a quick post as it's 3:20am and I've been working on this since 8:00pm last night!

Regular visitors will no doubt have noticed that my sidebar widgets have gone. The reason for this is quite simple. They write cookies without asking. As most people will realise, this is a no-no under GDPR.

Blogspot usefully provides a cookie that shows when a visitor agrees to the cookies usage banner and I've fixed up a fairly straightforward listener script that checks for the presence of this cookie. It works fine...   

The  idea is that where the widgets are I've put simple placeholder div tags and that once my listener verified a visitor has agreed to the use of cookies, to update the placeholder div tags with the third party provided scripts and thus load the Amazon and Twitter feeds.

The problem however is that it's not quite that easy....

Firstly, you can't just fudge it using document.getElementById and innerHTML to modify the div content, because browser security blocks this to prevent cross site scripting attacks. You have to do it properly using the DOM. 

This means using something along the lines of

var sc = document.createElement("script");
sc.setAttribute("src", "https://some");
sc.setAttribute("type", "text/javascript");
Which appends a script tag within the div itself. 

This pretty much works for most external scripts, and I've used this to good effect on several other sites....


With both the Amazon and Twitter feeds the script that is being called uses document.write to create content. This is bad... Bad because firstly it's a blocking method. As a synchronous write insertion it holds up the page load normally, but as we have now waited until after the page has loaded, and the visitor has agreed to cookies activating my listener script and kicking off the writing off the createElement script, the page has long ago loaded.... And document.write can no longer add to the current div... Doh!

What is needed is an asynchronous method of writing to the placeholder, but of course I have no control over the content of the third party script.

This makes life a lot more complicated!

So, at present I'm looking at using jQuery or an Ajax script to act as an asynchronous buffer for the third party script. This should solve the problem of insertion after page load is complete, but adds a lot of complexity.

I will do a full write up when this is finished, as I'm sure there will be a number of bloggers using Blogspot who are in the same position - having third party scripts that write cookies, but that they have no control over.

In the meantime, sidebar widgets will be off and the site may be a little odd while I run these tests.

As the BBC used to say: "Normal service will resume shortly, please do not adjust your sets" :)

More later...

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