Bad Argument JS

Terse, pure JavaScript function argument type checker. Implements contract pre-conditions for functions. Built for speed.

var argsMustBe = require('badargument');


function importantFunction(veryImportant, notImportant, thisMustBeAFunction) {
  argsMustBe('defined ignored function');

  whooohooo.some(code);
}

importantFunction('anyNonNullGoes', null, 'thisInsteadShouldBeAFunction');

Throws:

BadArgumentError: arg 2 of myImportantFunction is not a function.

Call arguments will also be stored in the Error's .arguments attribute.

Bad Argument uses Function.caller and will degrade gracefully if it is not available.

Default error conditions

• function or F: typeof arg !== "function"
• object or O: !(arg instanceof Object)
• number or N: typeof arg !== "number"
• string or S: typeof arg === "string" || arg instanceof String
• array or A: !Array.isArray(arg)
• truthy or t: !arg
• defined or *: arg == null
• ignored or _: false

As a guideline, single-char versions of conditions that test for type are uppercase letters.

Custom error conditions

var badargument = require('badargument');
function Banana(){}

var myArgsMustBe = badargument.factory(
  badargument.defaultTests(),
  {
    // This is more powerful
    B: {message: 'is not a banana', condition: function(arg) {return !(arg instanceof Banana)}},

    // This is faster because it gets inlined
    red: {message: 'is not red', condition: '!arg || arg.color !== "red"'}
  }
);


function picnic(howMany, appleType, where, callback) {
  myArgsMustBe('B red string function');
}

var apple = {color: 'blue'};
picnic(new Banana, apple, 'on the moon');

Will throw BadArgumentError: arg 1 of picnic is not red.