Javascript async function composition

Javascript async function composition

By : Joseph Plymouth
Date : November 21 2020, 07:31 AM
this will help Robert Rossmann is right. But I'm willing to answer purely for academic purposes.
Let's simplify your code to:
code :
Function.prototype.then = function (callback){ 
  var inner = this;
  return function (arg) { return inner(arg, callback); }
function getData(url, callback) {
Function.prototype.setCallback = function (c) { this.callback = c; }
Function.prototype.getCallback = function () { return this.callback; }

Function.prototype.then = function (f) {
  var ff = this;
  var outer = function () {
     var callback = outer.getCallback();
     return ff.apply(null, [].slice.call(arguments).concat(callback));

  if (this.getCallback() === undefined) {
  } else {

  return outer;

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Javascript\Kango: How to get a return of an async JS function inside a non-async function?

Javascript\Kango: How to get a return of an async JS function inside a non-async function?

By : Zephr Nine
Date : March 29 2020, 07:55 AM
Hope that helps You can't do it like this because of the async nature of generateID(). It will return BEFORE the async call has finished, thus the data is not available:
code :
data["userID"] = generateID();
generateID(function(val) {data["userID"] = val;});

function generateID(callback) {
kango.invokeAsync('kango.storage.getItem', 'userID', function(data) {
    uid = data;

    if (!uid) {
      console.log("uid doesn't exist, creating uid!");
      kango.invokeAsync('kango.storage.setItem', userID, function(data) { callback(data); });
    } else {
      console.log("uid found!: " + uid);

Function composition in JavaScript

Function composition in JavaScript

By : user3263480
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , For one, it's easier to read. Performance is rarely more important than that. Also, you could make a dedicated arity 2 function with nearly the same performance.
The other benefit is the composition can be easily changed at runtime. You can create versions that trim before capitalization, capitalize before trimming, trim only, capitalize only, or neither, without having to explicitly specify every single combination in the code. This can greatly simplify your code sometimes. Runtime composition is one of those things you never knew you always wanted.
code :
var c = function(x) {return x;} // identity
var onTrimClick          = function() {c = compose(c, trim);}
var onCapitalizeClick    = function() {c = compose(c, capitalize);}
var onSomethingElseClick = function() {c = compose(c, somethingElse);}
Function Composition: Augmenting an existing function with additional function in Javascript

Function Composition: Augmenting an existing function with additional function in Javascript

By : asubtlemind
Date : March 29 2020, 07:55 AM
this one helps. If you pass logThis() into your compose() function, you will hold a reference to it in the closure, so it will live on when you make a new logThis(). The name isn't really that important so long as you rename in an order that lets you get the reference to the old logThis() before you point the name at a new function. For example, the right side of logThis = compose(logThis, logThat) runs before the name assignment below, so you capture the function reference before reassigning the name:
code :
function logThis() {console.log('this')};
function logThat() {console.log('that')};

let compose = (f1, f2) => () => {

logThis = compose(logThis, logThat)
How Javascript `reduce` performed on function array achieves function composition?

How Javascript `reduce` performed on function array achieves function composition?

By : user2571570
Date : March 29 2020, 07:55 AM
seems to work fine I came across this pattern in redux compose function. I still don't understand how in the example below the functions are evaluated starting from the last and not from the first: , Let's step through the code with a very simple example:
code :
 compose(f2, f3, f4)
 y { // closure of y
  a -> y { // a references another closure of y
    a -> f3,
    b -> f2
  b -> f4
 a         (  b(...args))   
 y { ... } (  f4(2) )
 a (  b ( ...args))
 f2( f3( f4( 2 ) ) )
How to access root context from a composition function in Vue Composition API / Vue 3.0 + TypeScript?

How to access root context from a composition function in Vue Composition API / Vue 3.0 + TypeScript?

By : user3335287
Date : March 29 2020, 07:55 AM
this one helps. Well, I soon found out a proper example on that same RFC site. But decided to share my examples here.
The RFC site doesn't include examples in TypeScript at the moment, for clarity's sake I presume. As this new way of writing Vue 3.0 components and composition functions (as a replacement to Mixins) takes a bit of getting used to.
code :
// File: @/util/notify.ts
import { SetupContext } from '@vue/composition-api';

export function useNotify(context: SetupContext) {
  const notifyError = (title: string, msg: string) => {
    context.root.$bvToast.toast(msg, {
      variant: 'danger'

  return { notifyError};

export default useNotify;
// Use in your functional component:
import { createComponent, SetupContext } from '@vue/composition-api';

import { useNotify} from '@/util/notify';

export default createComponent({
  name: 'MyFailingComponent',
  setup(props: any, context: SetupContext) {
    const { notifyError } = useNotify(context);

    notifyError('Request error', 'There was an error processing your request, please try again later.');

    return {};
// File: @/util/notify.ts
import { SetupContext } from '@vue/composition-api';

export function useNotify({ context, defaultTitle = 'Hey!' }: { context: SetupContext, defaultTitle?: string }) {
  const notifyError = (msg: string, title?: string) => {
    context.root.$bvToast.toast(msg, {
      title: title || defaultTitle,
      variant: 'danger',

  return {

export default useNotify;

// Usage like:
const { notifyError } = useNotify({ context });
// Or
const { notifyError } = useNotify({ context, defaultTitle: 'Hey there' });
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