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map function parameters to types


$ npm install mapargs


Stop manually writing mapping and validation logic. Stop it right now. It's brittle and not fun.

var mapArgs = require('mapargs')

var listDocuments = mapArgs(function (authorId, skip, limit) {
  // do stuff
}, {
  authorId: Number,
  skip: {$map: Number, $optional: true, $default: 0},
  limit: {$map: Number, $optional: true, $default: 100}

This returns a function which we can call either with positional arguments (like the original), or named arguments by passing in an object with property names matching the parameter names.

listDocuments({name: 'f43', skip: '100'})
// equivalent to calling the original function with
// fn(43, 100, 100)

Use this when wiring up user input to application logic. Separate your gnarly HttpRequest objects from your core domain functions. Automatically map objects to their constructors.


mapArgs(fn: Function, mapObj?: Object) => Function

Returns a function which accepts named arguments and (optionally) has validation and defaults specified in mapObj

var add3 = function (a, b, c) {
  return a + b + c

var named = mapArgs(add3)

named({a: 1, b: 2, c: 3})
// => 6

mapObj should have property names corresponding to fn's parameter names. The values should be either mapping functions to be applied to the matching argument or an options object.

mapArgs.validate(mapObj: Object) => Function

Returns a function which will apply all of the validation and default logic and return an arguments object or throw an error.


$map: Function

A mapping function to be applied to the matching argument

$default: Value

A value used when the argument is not supplied or is undefined

$valid: Predicate Function

A function returning true if the argument is valid, false otherwise. mapArgs will throw an Error if the validation fails. Validation is run after the mapping function is applied.

$optional: Boolean

If true, the parameter is optional. If a default is specified, it will be used if the argument is undefined. If there is no default specified and the parameter is not marked optional, an error will be thrown.

a note about booleans

We treat the built-in Boolean constructor liberally. Unlike native Boolean, not all non-empty strings evaluate to true. Instead, only strings which case-insensitively compare to t, true, y, or yes are true; otherwise they're false. And only numbers > 0 evaluate to true; otherwise they're false.

running the tests

change to package root directory

$ npm install
$ npm test





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