wait-for-stuff
an extendable library that can wait for stuff to happen in a synchronous-but-not-blocking manner
Last updated 2 years ago by ujc .
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wait-for-stuff

An extendable library that can wait for stuff to happen in a synchronous-yet-non-blocking manner.
Instead of waiting for async\await, you can now simply wait for the following "stuff":

  • time (wait for x seconds to pass)
  • date (wait until date is reached)
  • predicate (wait until prediacte returns true)
  • event (wait until event emits)
  • promise (wait for promise to settle)
  • generator (wait for generator to fully exhaust all values)
  • stream (wait until readable-stream is fully read)
  • callback (wait for node-style callback to be called)
  • function (wait for custom callback function to be called)
  • yield (wait for a generator to yield a speific value)
  • value (wait for object.property to equal value)
  • property (wait for object.property to exist)
  • array (wait for array to contain some value)
  • compose (compose a new waiter from two or more existing waiters)
  • result (wait for a chain of waitables to return a non-waitable result)

Table of Contents

  1. Why?
  2. Install
  3. How it works
  4. Built-in waiters
    1. wait.for.time()
    2. wait.for.date()
    3. wait.for.event()
    4. wait.for.predicate()
    5. wait.for.promise()
    6. wait.for.generator()
    7. wait.for.stream()
    8. wait.for.callback()
    9. wait.for.function()
    10. wait.for.yield()
    11. wait.for.value()
    12. wait.for.property()
    13. wait.for.array()
  5. Middleware
    1. wait.use()
    2. wait.alias()
  6. Composition
    1. wait.compose()
    2. wait.for.result()
  7. Contribute
  8. Test
  9. Related

# Why ?

Because I'm tired of waiting for await\async, and want this code to work
(without blocking node's event-loop):

var fs   = require('fs');
var wait = require('wait-for-stuff');

var myFile   = fs.createReadStream('my.json');
var contents = wait.for.stream(myFile);

// the stream has now been fully read, async in the
// background while my code is still nice-and-pretty, without
// worrying about async-code-execution-flow design patterns
// and such

// feel free to do something with the file contents now



# Install

npm install wait-for-stuff



# How it works

Behind the scenes, wait-for-stuff uses deasync to do it's magic.
This basically means that you can write your code in a linear, sequential manner - while still allowing async operations to complete in the background on the same execution block.



# Built-in waiters

wait-for-stuff is designed to be middleware-oriented - which is just a fancy way of saying you can add your own "stuff" to "wait for" based on your own logic.
That said, it also comes with the following built-in waiters:



# wait.for.time(seconds)
Waits until seconds number of seconds pass

wait.for.time(3);
// 3 seconds have now passed



# wait.for.date(futureDateObject)
Waits until the system time passes the date of futureDateObject.

futureDateObject must be a Date object.
If futureDateObject is configured as a date that has already passed, the waiting will simply end immediately.

var theFuture = new Date( new Date().getTime() + 5000 );
wait.for.date(theFuture);
// we are now in the future (though just by 5 seconds, so no biggy)



# wait.for.event(emitter, eventName)
Waits until emitter emits the eventName event.
Returns the data that the event emitted (if any).

var eventData = wait.for.event(myEmitter, 'someEvent');

// if the event was emitted with just a single data argument,
// <eventData> will get that value

// if the event was emitted with multiple data arguments,
// <eventData> will be an array with those data arguments



# wait.for.predicate(fn)
Waits until the predicate function returns a truthy value.
This is useful if you need a simple mechanism to wait on your own custom application logic

var isDone = false;
setTimeout(() => isDone = true, 5000);

wait.for.predicate(() => isDone);
// [5 seconds later]: isDone is now true, execution continues



# wait.for.condition
Same as wait.for.predicate.
This is just a convenience alias in case you prefer to use the word "condition" instead of "predicate"



# wait.for.promise(promise)
Waits until promise is settled (either resolved or rejected).
Returns the value that the promise was settled with.

var resultOrError = wait.for.promise(new Promise(...));



# wait.for.generator(generator)
Waits until the generator has fully exhausted all of it's yielded values.
Returns the value that the generator function returns.

generator can either be a generator-function, or an actuale iterable-generator (the result of a generator-function)

function* myGeneratorFunction(){
    count = 0;
    while (count < 10) { yield ++count }
    return 'complete!';
}

var result = wait.for.generator(myGeneratorFunction);
// result === 'complete!'


//////////////////////////////////////////////////////
// alternative (pass in the actual iterable-generator)
function* myGeneratorFunction(){
    count = 0;
    while (count < 10) { yield ++count }
    return 'complete!';
}

var iterable = myGeneratorFunction();
var result   = wait.for.generator(iterable);
// result === 'complete!'



# wait.for.stream(readableStream)
Waits until readableStream has been fully read (ended).
Returns the data that was read from the stream
(either as string or buffer, based on what the stream emitted as it's chunks)

var myFile       = fs.createReadStream('someFile.json');
var fileContents = wait.for.stream(myFile);
// fileContents now contains the contents of someFile.json



# wait.for.callback(nodeAsyncFunction, ...params)
Waits until the nodeAsyncFunction has finished, passing to it any params that you supply.
Returns one or more values that the callback got as it's arguments.

If the callback got just a single value, that value will be returned by wait.for.callback() (usually either an error object or actual data).
If the callback got more than a single value, an array-of-values is returned by wait.for.callback(). This array-of-values filters out null and undefined values. The order of the items in the array is the order in which they were passed into the callback.
Also, if the after filtering for null and undefined values the array only contains a single element, that element is returned directly (instead of returning an array with just a single element in it).

NOTE: If you want to always get an array as the return value, use # wait.for.function()

// instead of this:
// -----------------------------------------------
// fs.readFile('foo.json', function(err, data){
//     do something with err or data
// });
// -----------------------------------------------

var errOrData = wait.for.callback(fs.readFile, 'foo.json');


///////////////////////////////////////////////////////
// or, if unlike fs.readFile, the function may pass
// more than just "err" or "data":

// instead of this:
// moreComplexFunc('foo.json', function(err, data1, data2, data3){
//     do something with err, or data1 + data2 + data3
// });

var errOrResultSet = wait.for.callback(moreComplexFunc, 'foo.json');

// errOrResultSet will either be 'err',
// or an array containing [data1, data2, data3] in order



# wait.for.function(customAsyncFunction, ...params)
Waits until the customAsyncFunction has finished, passing to it any params that you supply.

Unlike wait.for.callback(), any-and-all arguments that were passed into the function will be returned as the complete resultSet of the customAsyncFunction.

// instead of this:
// -----------------------------------------------
// fs.readFile('foo.json', function(err, data){
//     do something with err or data
// });
// -----------------------------------------------

var resultSet = wait.for.function(fs.readFile, 'foo.json');

// resultSet is an array of [err, data] in order



# wait.for.yield(generator, value)
Waits until the generator has yielded the specified value.

generator can either be a generator-function, or an actuale iterable-generator
(the result of a generator-function)

function* myGeneratorFunction(){
    count = 0;
    while (true) { yield ++count }
}

wait.for.yield(myGeneratorFunction, 5);
// count is now 5


//////////////////////////////////////////////////////
// alternative (pass in the actual iterable-generator)
function* myGeneratorFunction(){
    count = 0;
    while (true) { yield ++count }
}

var iterable = myGeneratorFunction();

wait.for.yield(iterable, 5);



# wait.for.value(owner, property, valueToWaitFor)
Waits until the owner[property] matches valueToWaitFor.

property must be a string
owner must be an object

var myObject = { foo: 'bar'};
setTimeout(() => myObject.foo = '123', 5000);

wait.for.value(myObject, 'foo', '123');
// [5 seconds later]: myObject.foo now equals '123'



# wait.for.property(owner, property)
Waits until owner has a property named property

property must be a string
owner must be an object

var myObject = {};
setTimeout(() => myObject.foo = true, 5000);

wait.for.property(myObject, 'foo');
// [5 seconds later]: myObject now has a property named 'foo'



# wait.for.array(array, value)
Waits until array contains value

var myArray = [];
setTimeout(() => myArray.push('hello world'), 1000);

wait.for.array(myArray, 'hello world');




# Middleware

This library aims to provide atomic structures with the built-in waiters.
From these, you can construct any custom waiter for anything additional that you may need in your application.

Once you've built your own waiter-middleware - or installed third-party waiter-middleware - you can add it to wait-for-stuff using the wait.use(name, middleware) api.



# wait.use(name, middleware)
Adds middleware as a waiter that can be used with the general wait.for... API, under wait.for.<name>.

var wait = require('wait-for-stuff');

wait.use('minutes', minutes => {
    wait.for.seconds(minutes * 60);
    return;
});


// later on in your code, when you need to wait for X minutes
// to pass - which totally makes sense in node applications (;
wait.for.minutes(2);
// [2 minutes later]: code execution continues



NOTE: You can also use this api to overwrite existing waiters with your own logic.
While this is possible to do, it is not recommended.



# wait.alias(originalName, alias)
Allows you to create an alias of your own liking to an existing waiter.
For example, wait.for.condition() is just an alias to wait.for.predicate().

wait.alias('promise', 'syncPromise');
wait.for.syncPromise(myPromise);  // just an alias to "wait.for.promise()"




# Composition

You can compose an advanced waiter by combining the work of two or more waiters together.
This is done using wait.compose(waiter1, waiter2, ...waiterN).
The result is a new waiter that passes the return value from one waiter to the next, until all waiters have completed.

# wait.compose(waiter1, waiter2, ...waiterN)
Composes a new waiter from the waiters that are passed in.
Waiters are exhausted from right-to-left - just like you would expect from the functionl-programming compose function

function myComplexFunction(path, callback){
    fs.exists(path, result => {
        var stream = fs.createReadStream(path);
        callback(stream);
    });
};

// first we create a composed waiter
// it will first expect the arguments that should be passed into >wait.for.callback.
// the result of wait.for.callback is then passed into wait.for.stream.
// the final result is what wait.for.stream will have returned
//
// in our case, myComplexFunction() expects a callback, which then gets >a stream
// composition allows us to wait on both 'waiters'
var streamAndCallbackWaiter = wait.compose('stream', 'callback');
var result                  = streamAndCallback(myComplexFunction, __filename); // arguments for wait.for.callback

// result is the return value from wait.for.stream



# wait.for.result(waitable))
Waits until a chain of waitables return a non-waitable result.
For example, if you need to wait on a promise that returns another promise that returns a stream - you can just wait for the result of the final stream using wait.for.result.

waitable can be any of the following:

  • Promise
  • Generator (or the iterator-result of a generaotr)
  • Stream
// a promise that returns a promise that returns a stream
var myComplexPromise = new Promise((res, rej) => {
    setTimeout(() => {
        res(new Promise((res, rej) => {
            setTimeout(() => res(fs.createReadStream('someFile.json')), 500);
        }));
    }, 500);
});

var result = wait.for.result(myComplexPromise);
// result is now a buffer holding the contents of 'someFile.json'



# Contribute

I hope people will find this module helpful - either as an alternative to asynchronous flow-execution patterns such as await\async (until it's official release at least) - or as a supplement to go along with what ever you're all ready using.

If you create your own waiter-middlewares, please do share them with the community.
If you would like to have your waiter middlware added as a built-in to wait-for-stuff, please send a PR (please also make sure to include tests)



# Test

npm run test



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