argsy

awesome argument assertion

Made with ❤ at @outlandish

Argument-oriented assertions...

• assertions that name offending arguments
• collects assertion failures and groups them in a single error
• reports function name, location, and clean stack trace
• support for optional arguments

Example

Before

function hello (name, message) {
  if (typeof name !== 'string' || !name.length) {
    throw new Error('expecting name to be non-empty string')
  } else if (message && typeof message !== 'string') {
    throw new Error('expecting message to be string')
  }
  console.log('hello', name, message)
}
hello() //=> Error: expecting name to be non-empty string

After

function hello (name, message) {
  assert('hello')
    .nonEmptyStr(name)
    .optional.str(message)
  console.log('hello', name, message)
}
hello()
//=>  Error: Failed argument assertions in call to "hello" at C:/hello.js:1:
//      - expecting name to be non-empty string

Install

npm install --save argsy

yarn add argsy

Import

// ES2015
import assert from 'argsy'

// CommonJS
var assert = require('argsy')

API

assert.{method}(val[, subject][, name[, name2]])

Assert val is of type indicated by method (see below).

• val {*} value to assert
• subject {*} (optional) subject of assert
• name {String} name to report in error message
• nam2 {String} (optional) name of subject

No return value.

AssertionInstance

assert([name]) : AssertionInstance

Create a new assertion instance.

• name {String} (optional) name of the assertion instance

Returns an AssertionInstance.

AssertionInstance.{method}(val[, subject][, name[, name2]])

Assert val is of type indicated by method (see below).

• val {*} value to assert
• subject {*} (optional) subject of assert
• name {String} name to report in error message
• nam2 {String} (optional) name of subject

Returns the AssertionInstance.

Methods

ok
notOk
str
obj
nonEmptyStr
num
sym
int
bool
undef
null
nan
elem (use subject arg)
key (use subject arg)

AssertionInstance.optional.{method}()

Assert an optional value.

Shares the same API as AssertionInstance.method (see above).

Returns the AssertionInstance.

AssertionInstance.$eval()

Assert the arguments.

This should be called last in the chain of assertion declarations.

More Examples

examples/report.js

Evaluates all assertions, groups them, and reports all failures.

Note call to $eval at the end.

function add (a, b) {
  assert('add')
    .num(a, 'a')
    .num(b, 'b')
    .$eval()
    
  return a + b
}

const a = Number(process.argv[1])
const b = Number(process.argv[2])
const result = add(a, b)

console.log(a, '+', b, '=', result)

Good

$ node examples/add.js 1 2
1+2=3

Bad

$ node add.js
Error: Failed argument assertions in call to "add" at C:/argsy/examples/report.js:10:
  - expecting a to be number
  - expecting b to be number
    at Function.evaluate (C:/argsy/src/index.js:63:13)
    at add (C:/argsy/examples/report.js:10:6)
    at Object.<anonymous> (C:/argsy/examples/report.js:18:16)

examples/spongebob.js

Stops and throws at first failed assertion.

import assert from 'argsy'

function person (name, occupation) {
  assert
    .nonEmptyStr(name, 'name')
    .optional.nonEmptyStr(occupation, 'occupation')

  console.log(name + ' is a ' + (occupation || 'sponge'))
}

person('Spongebob')
//=> Spongebob is a sponge

person(['Spongebob'], 'crabby patty flipper')
//=> Error: Expecting name to be a non-empty string

person('Spongebob', 'crabby patty flipper')
//=> Spongebob is a crabby patty flipper

Contributing

All pull requests and issues welcome!

If you're not sure how, check out the great video tutorials on egghead.io!

License

MIT © Sam Gluck