JS: Exclude null values from resolved value

readme.md

why

This comes in handy when a callback function returns 2 things: undefined or Promise. This happens when:

• Callback may return undefined when confirmation dialog (window.confirm) is cancelled.
• Otherwise, just proceeds, and finally callback returns a Promise which does the ajax request

function callback(id) {
  if (!confirm('Are you sure to delete?')) {
    return;
  }
  
  return axios.delete(`/products/${id}`);
}

before

Promise.resolve(promise)
  .then(res => {
    return !res
  })
  .then(res => {
    // Do something
  });

after

resolve(promise)
  .then(res => {
    // Do something
  });

footguns

Careful, if you don't return something inside a then, you're going to waste a lot of time why your program's acting weird.

// bad
function callback(id) {
  if (!confirm('Are you sure to delete?')) {
    return;
  }
  
  return axios.delete(`/products/${id}`)
    .then(res => {
      // do something
      // not return
    });
}

// good
function callback(id) {
  if (!confirm('Are you sure to delete?')) {
    return;
  }
  
  return axios.delete(`/products/${id}`)
    .then(res => {
      // do something
      return res;
    });
}

index.js

function resolve(promise) {
  return Promise.resolve(promise)
    .then(res => {
      return res
        ? res
        : Promise.reject();
    })
}