Cancel a Promise

cancellable.js

// Adapted from:
// https://facebook.github.io/react/blog/2015/12/16/ismounted-antipattern.html
function cancellable(promise) {
    let cancelled = false;
  
    // Creates a wrapper promise to return. This wrapper is
    // resolved or rejected based on the wrapped promise, and
    // on the "cancelled" value.
    const promiseWrapper = new Promise((resolve, reject) => {
      promise.then(
        value => {
          return cancelled ? reject({ cancelled: true }) : resolve(value);
        },
        error => {
          return cancelled
            ? reject({ cancelled: true })
            : reject(error);
        }
      );
    });
  
    // Adds a "cancel()" method to the promise, for
    // use by the React component in "componentWillUnmount()".
    promiseWrapper.cancel = function cancel() {
      cancelled = true;
    };
  
    return promiseWrapper;
  }