Comma usage
I got these sentences from an internet source.

1. If it rains, you will get wet.
2. If Sally is late again I will be mad.
3. If you don't hurry, you will miss the bus.

How come Number 2 does not need a comma? Or is it also acceptable to write the sentence as "If Sally is late again, I will be mad."

Please clarify if you know the answer! Thank you very much :)

Question

Comma usage
I got these sentences from an internet source.

1. If it rains, you will get wet.
2. If Sally is late again I will be mad.
3. If you don't hurry, you will miss the bus.

How come Number 2 does not need a comma? Or is it also acceptable to write the sentence as "If Sally is late again, I will be mad."

Please clarify if you know the answer! Thank you very much :)

Answer

I would consider that the comma is missing in sentence 2 and as such does not follow standard rules. I guess in modern English and in common usage it would not affect meaning in most cases but it would be noticed by the majority of speakers.

How could it affect meaning? Well, the comma in English is often used to separate ideas. In the case where the 'IF' clause needs to be quite long and even convoluted a comma does indeed help!
Consider
If you and me were to go there on a Sunday at lunchtime we would have a great time.
If you and me were to go there on a Sunday at lunchtime, we would have a great time.
The second is much clearer. I cannot think of an example right now, but I imagine it would be possible to create a scenario where the missing comma would lead to some confusion!

Answer

https://www.ef.com/english-resources/english-grammar/punctuation/

There is a lot of garbage on the internet.  All three sentences need commas.