Qulity | A memory management utility

The code given in the question sort of assumes that things are happening synchronously.

The problem is that the call canvas.toBlob does not instantaneously create a blob, it uses a callback function when it has done so.

If you put console.log statements in the code, one just after the for and one in the callback function, you will see that the for loop finishes before any of the callback functions are executed.

What we need to do is get the first blob, check it, then if it's not suitable get the next one and so on

You can see an example at https://rgspaces.org.uk/blobtest.html - look at the Console log in dev tools.

Here's the code: