Learn English – would not have had

The sentence is a way of saying:

Angular is what HTML would have been if it had been designed for applications.

In general, phrases of the form "if [noun] [helping verb] [verb]" can be rewritten as "[helping verb] [noun] [verb]".

EDIT: As Colleen pointed out in her comment, helping verbs are also commonly called auxiliary verbs.

Examples:

• If I had been there, I could have stopped it. -> Had I been there, I could have stopped it.
• If John were taller, he could play basketball. -> Were John taller, he could play basketball.
• If the dog would jump, he could escape. -> Would the dog jump, he could escape.

• Had they had any savings they didn't need, they would've re-paid their son's student loan.
• If they had had any savings they didn't need, they would've re-paid their son's student loan.

Can I say:

Have I had any savings, I would pay my son's student loan.

If you look at the first two examples, you'll notice that they both use two 'had's. In the first example, we see subject-auxiliary inversion to show that the clause is subordinate, instead of using if. In old-fashioned style English, main verb HAVE is sometimes used as an auxiliary. This means we can use it to make questions and negatives and it can be used to form question tags for sentences using present simple or past simple verb forms instead of using the auxiliary DO:

• Have we any eggs?
• We haven't any eggs.
• We have eggs, haven't we?

We can also use the verb HAVE as an auxiliary verb in the Original Poster's example. We simply need to invert, change the order, of the subject and have. If we do this we don't use if. Notice too, that we don't need to add an auxiliary here. The 'main verb', have, actually is an auxiliary in this situation:

• Had I any savings, I would pay my son's student loan.

However! when you're learning English, it is very important to understand that main verb have does NOT usually behave like an auxiliary verb! Remember to use DO for questions and negatives when you use the past simple or present simple.

Hope this is helpful!