async3.js

Procedural asynchronous flow control for JavaScript in Node.JS and browsers.

For people who find continuation passing style (CPS) more reasonable than Promises, Futures, generators, etc.

Inspired by async2, mini-async.

Motivation

Javascript, like many languages that support passing callbacks to asynchronous APIs, provides flow control keywords (i.e, if, while, for) that are nearly useless once you need to await the future result.

At some point you realize you need to take a procedural approach and reimplement these keywords as functions.

In doing so, if you are familiar with assembly or machine code, you may realize that all flow control operations can actually be reduced to conditional JMP opcodes. Trendy variations like unless, until, do...while, etc. are unecessary syntactic sugar.

Taking the minimalist approach, you realize you can get a large degree of control with just a few functions that are a few lines of code each. No need for object instantiations, or multiple function calls in a builder pattern.

Include

ES6 Node.JS:

const {ifAsync} = require('async3');

Flow Control Functions

• ifAsync : conditional branching without two callback references
• whileAsyncSerial: latched infinite loop
• forEachAsyncSerial : serial one-at-a-time invocation
• forEachAsyncParallel : parallel branch-join invocation
• forEachAsyncParallelBatch : parallel with limited maximum concurrent invocations

Async3.ifAsync()

For when you have two functions: one that is asynchronous but is only executed sometimes, and one that is called afterward. Without this, you'd have to declare or reference the second function twice.

Syntax

void ifAsync(test, true_cb[, ...args], done_cb);

Parameters

• test
  Truthy value determines whether to invoke true_cb.

• true_cb
  The function invoked if the test function above returns truthy. Accepts no targ Expected to be asynchronous. Accepts arguments provided in ...args parameter described below. Void return value.

• ...args
  Optional. One or more arguments of any type, to be passed into true_cb function.

• done_cb
  Function invoked after true_cb completes. Invoked regardless of whether test returned truthy.

Example

ifAsync(tmpAbsPath != absPath,
  exec, 'mv "'+ tmpAbsPath +'" "'+ absPath +'"', () =>
{
  console.log('placed locally for later static upload to cdn as '+ relPath);
});