Google has recently changed it AdSense script. Or we can say that it had upgraded its ads unit script. Previously it had only synchronous type of script. But from last few days it had added new type of AdSense code script known as Asynchronous.
Currently, this Asynchronous script is under BETA phase i.e testing script in live user environment. Now let us discus what is difference between these two.
What is Synchronous AdSense Ads?
When you execute something synchronously, you wait for it to finish before moving on to another task. Same thing was happening in Adsense Ads previously.
Take a look at the script code in below image, explanation given after this.
In simple words it can be explained as below:
Ad2 is loaded only after completion on Ad1, similarly about Ad3 after Ad2 and so no.
What is Asynchronous AdSense Ads?
When you execute something asynchronously, you can move on to another task before it finishes. Same thing is now being applied to Ads by Google.
Take a look at the script image below, explanation after image.
Now once the JS file is loaded at the start of first ad it can simultaneously call other Ads space slot code.
In Simpler way it can be represented as;
This means before the end of Ad1, Ad2 will be started loading in browser, similarly with Ad3.
Best AdSense Ads script to use now?
As Asynchronous has benefit of loading all the ads at same time. This will improve loading speed of your site and reduce the server load.
Hence, I recommend to use Asynchronous ads for better and fast loading of ads.
But, as if now this type is in BETA phase of development. I would recommend to use it on any one of ads space of your 3 ads space for few days. If it works fine for you then shift all the script code to asynchrous. (Async is live to use, and it is recommended to use Async AdSense for better loading time of site)