Sometimes in certain accents and in more casual/informal speech, the words are slurred together. But it's the "did" that gets slurred into the previous word.
So, "How did you like it" becomes "how'd you like it?" (similarly "Where'd you go?"). Or from your book,
"How did" -> /hæo/
"you" -> /je/
When "Did" is at the beginning of the sentence, there's nothing for it to disappear into, so it's more fully pronounced. Does that make sense?