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A ridiculously light-weight function argument validator

var validate = require("aproba")function myfunc(a, b, c) {  // `a` must be a string, `b` a number, `c` a function  validate('SNF', arguments) // [a,b,c] is also valid}myfunc('test', 23, function () {}) // okmyfunc(123, 23, function () {}) // type errormyfunc('test', 23) // missing arg errormyfunc('test', 23, function () {}, true) // too many args error

Valid types are:

Validation failures throw one of three exception types, distinguished by acode property ofEMISSINGARG,EINVALIDTYPE orETOOMANYARGS.

If you pass in an invalid type then it will throw with a code ofEUNKNOWNTYPE.

If anerror argument is found and is not null then the remainingarguments are optional. That is, if you sayESO then that's like using anon-magicalE in:E|ESO|ZSO.

You can provide more than one signature by separating them with pipes|.If any signature matches the arguments then they'll be considered valid.

So for example, say you wanted to write a signature forfs.createWriteStream. The docs for it describe it thusly:

fs.createWriteStream(path[, options])

This would be a signature ofSO|S. That is, a string and and object, orjust a string.

Now, if you read the fullfs docs, you'll see that actually path can ALSObe a buffer. And options can be a string, that is:

path <String> | <Buffer>options <String> | <Object>

To reproduce this you have to fully enumerate all of the possiblecombinations and that implies a signature ofSO|SS|OO|OS|S|O. Theawkwardness is a feature: It reminds you of the complexity you're adding toyour API when you do this sort of thing.

This has no dependencies and should work in browsers, though you'll havenoisier stack traces.

I wanted a very simple argument validator. It needed to do two things:

1. Be more concise and easier to use than assertions

2. Not encourage an infinite bikeshed of DSLs

This is why types are specified by a single character and there's no suchthing as an optional argument.

This is not intended to validate user data. This is specifically aboutasserting the interface of your functions.

If you need greater validation, I encourage you to write them by hand orlook elsewhere.