JavaScript not waiting on promise to resolve

Question

In the following code, what I'm after is to get the alert, after the counting is finished in the setInterval. The alert shows first though, and then the counting happens. What have I done wrong?

function function1() {
  return new Promise((resolve, reject) => {
    console.log('in function1 ')
    function2().then(resolve());
  });
}

function function2() {
  return new Promise((resolve, reject) => {
    var x = 0;
    I = setInterval(function() {
      console.log(x);
      if (x > 10) {
        clearInterval(I);
        resolve()
      };
      x++
    }, 100);
  });
}

function1().then(alert('finished'));

The argument to `.then()` must be a function, not a call of the function. `.then(() => alert('finished'))` — Barmar, Sep 29 '21 at 20:59
@Barmar don't forget `function2().then(resolve());`, which is broken in a similar fashion. — canon, Sep 29 '21 at 21:01
[What is the explicit promise construction antipattern and how do I avoid it?](https://stackoverflow.com/q/23803743) — VLAZ, Sep 29 '21 at 21:01
Does this answer your question? [When do I use parenthesis and when do I not?](https://stackoverflow.com/questions/7969088/when-do-i-use-parenthesis-and-when-do-i-not) — Heretic Monkey, Sep 29 '21 at 21:03

score 1 · Accepted Answer · answered Sep 29 '21 at 21:02

Promise#then's first argument:

onFulfilled : A Function called if the Promise is fulfilled. This function has one argument, the fulfillment value. If it is not a function, it is internally replaced with an "Identity" function (it returns the received argument).

You can either pass a function name or a function as below:

function function1() {
  return new Promise((resolve, reject) => {
    console.log('in function1 ')
    function2().then(resolve); // onFulfilled
  });
}

function function2() {
  return new Promise((resolve, reject) => {
    var x = 0;
    I = setInterval(function() {
      console.log(x);
      if (x > 10) {
        clearInterval(I);
        resolve()
      };
      x++
    }, 100);
  });
}

function1().then(() => alert('finished')); // onFulfilled

JavaScript not waiting on promise to resolve

1 Answers1