using then() in promise

Question

I'm using promise in the block of code below, 2 first then() I dont return any value, so i wonder that is the function in the first then() called before the function in the next then(). Im using typescript in angular 2. Thank you :D

Promise.resolve()
    .then(()=>{
      this.getListStatus();
    })
    .then(()=>{
      return this._laundryServiceOrderService.findAll(true, offset, this.itemsPerPage, filterQuery)
    })
    .then((response) => {
      this.orders = response.data;
      this.totalItems = response.totalItems;
    })
    .catch(error => {
      FlashMessage.setError(error.message);
    });

Answer 1

first then() I dont return any value, so i wonder that is the function in the first then() called before the function in the next then().

Yes, it is. (This can trivially be checked with a debugger.)

It doesn't matter that it doesn't return a value; that's effectively the same as doing return undefined. So the next callback in the chain will see undefined as the resolution value, but since that next callback doesn't care about the resolution value, that's fine.

Here's a simple example demonstrating it:

Promise.resolve("a")
  .then(result => {
    console.log("First callback got: " + result);  // Gets "a"
  })
  .then(result => {
    console.log("Second callback got: " + result); // Gets undefined
    return "b";
  })
  .then(result => {
    console.log("Third callback got: " + result);  // Gets "b"
  })
  .catch(error => {
    console.log("There's no error above, this won't get triggered.");
  });