to-infinitive as a direct object(noun phrase)? (as in 'I promised to buy her a pizza tomorrow') [duplicate]

I'm a passionate Korean English-learner, and I would like to ask you a question about grammar.

It was 3 years ago when I first started to study the to-infinitive as studying grammar with Grammar In Use series and English Grammar series by Longman, having been exposed to English for 3 years. There wasn't any mention of the author saying that the usage of the to-infinitive is as an (direct) object. And for me also, the times I have encountered sentences in which the usage of the to-infinitive, so to speak, as direct objects were used, I've read them as some kind of obligatory adverbial that shows what the verbs are about, not as objects, which means they are noun phases! 100% of Korean textbooks say the usage is as a direct object, but I doubt it. I think it's some kind of obligatory adverbial that shows what the verbs are about.

I thought it was better for me to ask Americans themselves. Do you read this usage of to-infinitive as a noun phrase or an adverbial?

Your example sentence regarding a "promise to [...]" is of the direct object usage. "To get there in time" is the thing that was promised (in the abstract). Other examples of the direct object case are below. Notice these are all infinitives.

I sought to learn more.

She wanted to go.

He started to run.

However, there are plenty examples of a "to" preposition following a verb where the preposition is not an object. These are adverbial in nature. They modify the verb.

I ran to the store.

She called to the waiter.

He crawled to the finish line.

Typically infinitives when following transitive verbs will act as the direct object of the verb, while prepositions which follow intransitive verbs act as prepositional adverbs.