A tiny error-throwing module for checking types.
In a language like JavaScript where there is no compilation step, you have to be very consequent when it comes to make sure that certain parameter values are of a specific type or are available at all. If it does not, then it should be considered as a programmer error and must be thrown immediately.
Node.js ships with the awesome assert module which is very handy in this use case. Anyways, when you use it intensively you will discover that the handling of edge cases has to be done manually (like checking if a value is a real object (JS does treat arrays and objects equally as object)). With assert you have to do something like
assert.equal('object' === typeof param && !util.isArray(param), true, '"param" should be a real object.');Using raw asserts will mess up your code quickly. This is where mandatory enters the stage:
mandatory(param).is('object');It uses the assert module internally and wraps it into a minimalistic API. Like assert, it throws error objects which is cool, because passing wrong parameters is a programmer error which should fail fast.
npm install --save mandatory'use strict'
var mandatory = require('mandatory');
exports.doSomething = function doSomething (id, options, foo, callback) {
mandatory(id).is('number');
mandatory(options).is('object');
mandatory(foo).is('array', '"foo" should be a real array');
mandatory(callback).is('function');
...
};expectedTypestring, number, object, array, functionmessage(optional) A custom error message. Otherwise mandatory will respond with a default error message, like 'Expected "object", but received "array"'
In a typed language with a compile phase you benefit from the execution of those checks in this phase. By checking it on every function execution it is crucial that those checks have to be fast. The gulpfile comes with a suite which tests mandatory's performance. You can initiate it by executing gulp benchmark. This is one result:
index.performance x 149,332 ops/sec ±6.96% (79 runs sampled)This shows that the assert module is pretty fast.
The MIT License (MIT) Copyright (c) 2014 konexmedia
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