A generic function definition and dispatch library for Javascript.
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A generic function definition and multi-dispatch library for JavaScript.

Multi-dispatch generic functions support the selection and execution of a function based on the types and number of arguments.

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npm install js-generics

The index.js and package.json files are compatible with node-require so that js-generics can be served directly to the browser from the node-modules/js-generics directory when using node Express.


Multi-dispatch generic functions support the selection and execution of a function based on the types and number of arguments. A common use is supporting mathematical operations on different types of objects. For example:

var sum = generic(function() { throw new Error("can't sum " + JSON.stringify(arguments)); } )
			 function(arg1,arg2) { return arg1 + arg2; })
	.method(function(arg) { return arg instanceof Array;},"number",
			 function(arg1, arg2) { arg1.forEach(function(item,i) { arg1[i] += arg2; }); return arg1; });

In the example above the generic function sum is defined to throw an error if no matching dispatch can be found. Matching dispatches have two arguments of type number or a first argument of kind array and a second of type number.

The general form of usage is:

generic(<default function>).method(<type matcher>[,<type matcher>...],<function to call>)[.method(<type matcher>[,<type matcher>...],<function to call>),...]

<default function> - This function is called if no matching dispatches are found. It can take any form and is called as .apply(this,arguments). As a result generic functions can be included as methods on objects.

<type matcher> - These should be primitive type names or functions. If a function, it's sole responsibility is to return true or false if the argument type is correct. The number of <type matcher> must match the number of arguments to <function to call>, or the last <type matcher> must be the special value generic.VARGS.

<function to call> - This function does the desired work. It is called as <type matcher>.apply(this,arguments).

.method calls can be chained and the last matching method is the one invoked by the dispatcher.

Release History (reverse chronological order)

v0.0.6 2016-01-03 Corrected markdown issues is README.

v0.0.5 2016-01-03 Added unit tests and documentation.

v0.0.4 2015-12-13 Codacy improvements

v0.0.3 2015-12-13 Initial public commit.


MIT License - see LICENSE file