When-conditional

A utility library for asyncronous conditional checking, and then running a callback when the condition is true.

To get started, type the following:

npm install when-conditional

Syntax

when(logicStatement, callback)

Parameters

logicStatement

A function which should return a truthy statement. The return is equivalent to what you would put in an if statement.

callback

A function which is called when the logicStatement function returns a truthy value.

Returns a when object with 4 functions:

whenObj.clear(): A function to clear the when statement, if you don't want to wait for the condition to be true anymore.

whenObj.reset(): This is for when you need reset the whenObj after it fired the code, and wait for the same condition again.

whenObj.setCondition(newCondition): Overwrite the condition function you passed in on creation.

whenObj.setCode(newCode): Overwrite the code function you passed in on creation.

Examples

The example code shown below will print out someVar is false a number of times until it becomes true, then will tell you its true and exit.

var when = require('when-conditional');
var someVar = false;

var interval = setInterval(function(){
  console.log("someVar is " + someVar);
  if(someVar === true) clearInterval(interval);
}, 1000);

when(function condition(){
	return (someVar === true);
}, function code(){
	console.log("someVar is now true, and this was only triggered when it became true!");
});

setTimeout(function(){
	someVar = true;
}, 10000);

Removing the when listener

You might feel that you no longer need to wait for something to happen. if this is the case, you can call a .clear() function on the return value of when(condition, code).

The following example is very similar to the one above, but will never print someVar is now true, and this was only triggered when it became true! as it is no longer waiting for when someVar is true!

var when = require('when-conditional');
var someVar = false;

var interval = setInterval(function(){
  console.log("someVar is " + someVar);
  if(someVar === true) clearInterval(interval);
}, 1000);

var whenObj = when(function condition(){
	return (someVar === true);
}, function code(){
	console.log("someVar is now true, and this was only triggered when it became true!");
});

setTimeout(function(){
	someVar = true;
}, 10000);

setTimeout(function(){
  whenObj.clear();
}, 5000);

reseting the when listener and changing the code callback.

var when = require('when-conditional');
var someVar = false;

var interval = setInterval(function(){
  console.log("someVar is " + someVar);
  if(someVar === true) clearInterval(interval);
}, 1000);

var whenObj = when(function condition(){
	return (someVar === true);
}, function code(){
	console.log("someVar is now true, and this was only triggered when it became true!");
});

setTimeout(function(){
	someVar = true;
}, 10000);

setTimeout(function(){
  whenObj.clear();
}, 5000);

setTimeout(function(){
  whenObj.reset();
  whenObj.setCode(function newCodeCB(){
	  console.log("someVar is now true, and this was only triggered when it became true, AND after the when was reset AND after the code callback was changed!");
  });
}, 8000);

Contributing

If you feel there is a feature missing you would like to see, or an issue, feel free to log an issue on Github, or even better, send a PR! :D

Inspiration

I wanted an asyncronous if statement that only fired once the condition became true, but I couldn't extend the engine natively.

The example code above should similar to something like:

var someVar = false;

when(someVar === true){
	console.log("someVar is now true, and this was only triggered when it became true!");
}

setTimeout(function(){
	someVar = true;
}, 10000)

To get my little shim working, I check the condition every tick. this is not ideal. ideally, I want to Object.observe the conditions, and only fire the when check once when the conditions have been observed to change

The when-method module is expected to be more efficient than an interval.

See you when-ever!

Copyright Glen Keane - 2015 - MIT Licence