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Promise Extensions

promise.tap(fulfilled?: Function , rejected?: Function) => Promise

• A pass-through that gives access to the current value

//Warning: Modifies the Promise prototype
Promise.prototype.tap = function (onFulfilled, onRejected) {
  return this.then(
    (result) =>
      onFulfilled
        ? Promise.resolve(onFulfilled(result))
            .then(() => result)
        : Promise.resolve(result)
    ,
    (reason) => {
      onRejected
        ? Promise.resolve(onRejected(reason))
            .then(() => Promise.reject(reason))
        : Promise.reject(reason)
    }
  )
}
const yell = (words) => console.log(`${words.toUpperCase()}!!!`)
const log = (value) => console.log(value)
const logError = (reason) => console.error(reason)

Promise.resolve('Roar!').tap(yell).then(log)
Promise.reject(new Error('Timed Out')).tap(log, logError)

promise.always(fulfilled?: Function , rejected?: Function) => Promise

• Do something on settled. (fulfilled or rejected)

//Warning: Modifies the Promise prototype
Promise.prototype.always = function (onSettled) {
  return this.then(
    (value) => Promise.resolve(onSettled())
      .then(() => value),
    (reason) => onSettled()
      .then(() => Promise.reject(reason)))
}

takeALongTimeToLoad().always(hideLoadingIndicator)

Promise.Map(values: Array, predicate: Function) => Promise

Promise.Reduce(values: Array, predicate: Function, accumulator: Any) => Promise

Promise.Filter(values: Array, predicate: Function) => Promise