function.signature.extender


Allows to extend the signature of any function with new arguments.

The new arguments are appended at the start of the signature:

fx(arg1, arg2) ==> add new1 ==> fx(new1, arg1, arg2)

Use case: you write a automaton plugin extending a application
object using state templates that overwrite the app methods when they are activated. A state method is added to
query the current state, but the object has no changeToState method:

- methods should still run in app context in order to have this still referencing the app Object
- A state method is added to the app Object to query the current state, but the object has no changeToState method - user of app should not be able to change the state themselves
- developers should be able to use changeState in their state method bodies, but should not be bothered with handling it

Context and closures are useless here, we have to inject the changeToState at runtime to make it available in the body.

// developer writes
function stateMethod (arg1, arg2) {
if (condition) {
changeToState(xyz); // should to an error here
}
}

// loading state modifies signature (purpose of the function.signature.extender)
function changedStateMethod (changeToState, arg1, arg2) {
if (condition) {
changeToState(xyz); // changeToState now exists in run context
}
}

// call to someMethod does
app.someMethod = function () {
arguments[arguments.length] = automatonLib.changeToState;
return changedStateMethod.apply(arguments); // code runs without error
}

Usage

Set dependency

npm install function.signature.extender --save

Extend function signature

var signatureExtender = require('function.signature.extender');

// add one new argument
var newSimpleFunction = signatureExtender(simpleFunction, 'myNewArgument');

// add multiple new arguments
var newMultiFunction = signatureExtender(multiFunction, ['myNewArgument', 'andAnother]);

Inject value

arguments[arguments.length] = 'value for myNewArgument';
newSimpleFunction.apply(arguments);

arguments[arguments.length] = 'value for andAnother';
newMultiFunction.apply(arguments);

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Copyright (c) 2014 Luscus (luscus.redbeard@gmail.com)

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