Duck-Typed Value Handling for JavaScript

Ducky is a small Open-Source JavaScript library, providing Duck-Typed Value Validation, Value Selection and Flexible Function Parameter Handling. It can be used in Node.js based server and browser based client environments.

You can conveniently get Ducky in various ways:

• NPM: install as server component via the Node Package Manager:
  $ npm install ducky

• Git: directly clone the official repository:
  $ git clone https://github.com/rse/ducky.git

• cURL: download only the main file from the repository:
  $ curl -O https://raw.github.com/rse/ducky/master/lib/ducky.browser.js

Ducky provides the following API:

The version of Ducky, provided as a tuple of separate pieces, for easy comparison.

if (!(ducky.version.major >= 2 && ducky.version.minor >= 0))
    throw new Error("need at least Ducky 2.0.0");

Register under name an additional host or application type, represented by the constructor function type. This allows ducky.validate() and ducky.params() to validate objects which are instances of the type.

var Foo = function () { ... };
ducky.register("app.Foo", Foo);
ducky.validate(new Foo(), "app.Foo");

The following host types are pre-registered by default (if actually existing in the particular native or "polyfilled" host environment): Object, Boolean, Number, String, Function, RegExp, Array, Date, Error, Set, Map, WeakMap, Promise, Proxy and Iterator.

Unregisters the additional host or application type, which was previously registered under name with ducky.register().

ducky.unregister("app.Foo");

Dereference into (and this way subset) object according to the path specification and either return the dereferenced value or set a new value. Object has to be a hash or array object. The path argument has to follow the following grammar (which is a direct JavaScript dereferencing syntax):

Setting the value to undefined effectively removes the dereferenced value. If the dereferenced parent object is a hash, this means the value is delete'ed from it. If the dereferenced parent object is an array, this means the value is splice'ed out of it.

ducky.select({ foo: { bar: { baz: [ 42, 7, "Quux" ] } } },
    "foo['bar'].baz[2]") // → "Quux"

In case caching of the internally compiled Abstract Syntax Tree (AST) is not wishes, you can perform the compile and execute steps of ducky.select individually:

Compile the selection specification path into an AST.

Select from object a value via ast and either return it or set it to the new value value.

Validate an arbitrary nested JavaScript object object against the specification spec. The specification spec has to be a string following the following grammar (which is a mixture of JSON-like structure and RegExp-like quantifiers):

The special key @ can be used to match an arbitrary hash element key.

ducky.validate({ foo: "Foo", bar: "Bar", baz: [ 42, 7, "Quux" ] },
    "{ foo: string, bar: any, baz: [ number+, string* ], quux?: any }") // &arr; true

If an empty errors array is given, use it to assemble detailed error messages in case of a validation failure.

In case caching of the internally compiled Abstract Syntax Tree (AST) is not wishes, you can perform the compile and execute steps of ducky.validate individually:

Compile the validation specification spec into an AST.

Validate object against ast and return true in case it validates. If an empty errors array is given, use it to assemble detailed error messages in case of a validation failure.

Handle positional and named function parameters by processing a function's arguments array. Parameter name is the name of the function for use in exceptions in case of invalid parameters. Parameter args usually is the JavaScript arguments pseudo-array of a function. Parameter spec is the parameter specification: each key is the name of a parameter and the value has to be an Object with the following possible fields: pos for the optional position in case of positional usage, def for the default value (of not required and hence optional parameters), req to indicate whether the parameter is required and valid for type validation (a validation specification string accepted by the validate>() method).

function config () {
    var params = ducky.params("config", arguments, {
        scope: { pos: 0, req: true,      valid: "boolean"           },
        key:   { pos: 1, req: true,      valid: /^[a-z][a-z0-9_]*$/ },
        value: { pos: 2, def: undefined, valid: "object"            },
        force: {         def: false,     valid: "boolean"           }
    });
    var result = cfg_get(params.scope, params.key);
    if (typeof params.value !== "undefined")
        cfg_set(params.scope, params.key, params.value, params.force);
    return result;
}
var value = config("foo", "bar");
config("foo", "bar", "quux");
config({ scope: "foo", key: "bar", value: "quux", force: true });

Manage configuration option objects. Parameter spec is the option object specification: each key is the name of a parameter (or a sub-path) and the value has to be an Array with a type specification accepted by the validate() method as its first element and optionally a default value as the second element. If no default value is given for an option, it has to exist on initial value merging. Value merging is performed either when the options parameter is given or method merge(options: Object): Object is called on the resulting option object.

function config (options) {
    var options = ducky.options({
        foo:      [ "string"           ],
        bar:      [ "boolean", false   ],
        quux:     [ "number",  1.2     ],
        sub: {
            foo:  [ "string",  "dummy" ],
            bar:  [ "boolean", false   ],
            quux: [ "number",  2.4     ]
        }
    });
    options.merge({ foo: "bar", sub: { bar: true } })
    options.merge({ sub: { quux: 4.8 } })
}

Copyright (c) 2010-2023 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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