95 lines
2.7 KiB
Markdown
95 lines
2.7 KiB
Markdown
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aproba
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======
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A ridiculously light-weight function argument validator
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```
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var validate = require("aproba")
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function myfunc(a, b, c) {
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// `a` must be a string, `b` a number, `c` a function
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validate('SNF', arguments) // [a,b,c] is also valid
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}
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myfunc('test', 23, function () {}) // ok
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myfunc(123, 23, function () {}) // type error
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myfunc('test', 23) // missing arg error
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myfunc('test', 23, function () {}, true) // too many args error
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```
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Valid types are:
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| type | description
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| :--: | :----------
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| * | matches any type
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| A | `Array.isArray` OR an `arguments` object
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| S | typeof == string
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| N | typeof == number
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| F | typeof == function
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| O | typeof == object and not type A and not type E
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| B | typeof == boolean
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| E | `instanceof Error` OR `null` **(special: see below)**
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| Z | == `null`
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Validation failures throw one of three exception types, distinguished by a
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`code` property of `EMISSINGARG`, `EINVALIDTYPE` or `ETOOMANYARGS`.
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If you pass in an invalid type then it will throw with a code of
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`EUNKNOWNTYPE`.
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If an **error** argument is found and is not null then the remaining
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arguments are optional. That is, if you say `ESO` then that's like using a
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non-magical `E` in: `E|ESO|ZSO`.
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### But I have optional arguments?!
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You can provide more than one signature by separating them with pipes `|`.
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If any signature matches the arguments then they'll be considered valid.
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So for example, say you wanted to write a signature for
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`fs.createWriteStream`. The docs for it describe it thusly:
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```
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fs.createWriteStream(path[, options])
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```
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This would be a signature of `SO|S`. That is, a string and and object, or
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just a string.
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Now, if you read the full `fs` docs, you'll see that actually path can ALSO
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be a buffer. And options can be a string, that is:
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```
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path <String> | <Buffer>
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options <String> | <Object>
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```
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To reproduce this you have to fully enumerate all of the possible
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combinations and that implies a signature of `SO|SS|OO|OS|S|O`. The
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awkwardness is a feature: It reminds you of the complexity you're adding to
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your API when you do this sort of thing.
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### Browser support
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This has no dependencies and should work in browsers, though you'll have
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noisier stack traces.
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### Why this exists
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I wanted a very simple argument validator. It needed to do two things:
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1. Be more concise and easier to use than assertions
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2. Not encourage an infinite bikeshed of DSLs
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This is why types are specified by a single character and there's no such
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thing as an optional argument.
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This is not intended to validate user data. This is specifically about
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asserting the interface of your functions.
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If you need greater validation, I encourage you to write them by hand or
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look elsewhere.
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