validate-function-params

JavaScript library that assists with function parameter validation at runtime, through an easy-to-use Fluent API.

Installation

$ npm install validate-function-params

Usage

The following examples demonstrate how to use this library.

Basic Usage

The simplest way to validate a function:

const { validate, validations } = require('validate-function-params');
 
const add = (a, b) => a + b;
 
const validAdd = validate(
  validations.firstParam.mustBe.number,
  validations.secondParam.mustBe.number,
)(add);
 
// This call will produce the following error
// Error: Function add(number, number)
// Error: 1st parameter must be of type number
// Error: 2nd parameter must be of type number
validAdd();
 
// This call will produce the following error
// Error: Function add(number, number)
// Error: 2nd parameter must be of type number
validAdd(1);
 
// This call will successfully return 3
validAdd(1, 2);

Object Method Validation

Similarly you can validate object methods the following way:

const { validate, validations } = require('validate-function-params');
 
class Dog {
  constructor() {
    const validBark = validate(
      validations.firstParam.mustBe.string,
      validations.secondParam.mustBe.number,
    )(this.bark);
 
    this.bark = validBark;
  }
 
  bark(sound, times) {
    for (let i = 0; i < times; i++) {
      console.log(sound);
    }
  }
}
 
const dog = new Dog();
 
// This call will produce the following error
// Error: Function bark(string, number)
// Error: 1st parameter must be of type string
// Error: 2nd parameter must be of type number
dog.bark();

You can optionally bind validate to a this context to have its constructor name appear in the error log:

const { validate, validations } = require('validate-function-params');
 
class Dog {
  constructor() {
    const boundValidate = validate.bind(this);
 
    const validBarkWithThis = boundValidate(
      validations.firstParam.mustBe.string,
      validations.secondParam.mustBe.number,
    )(this.bark);
 
    this.bark = validBarkWithThis;
  }
 
  bark(sound, times) {
    for (let i = 0; i < times; i++) {
      console.log(sound);
    }
  }
}
 
const dog = new Dog();
 
// This call will produce the following error
// Error: Function Dog.bark(string, number)  <-- Notice 'Dog.' appearing before the method name
// Error: 1st parameter must be of type string
// Error: 2nd parameter must be of type number
dog.bark();

Complex Validations

You can validate any number of specific parameters without listing the ones you do not care about:

const { validate, validations } = require('validate-function-params');
 
const complex = (...args) => {
  /*...*/
};
 
const validComplex = validate(
  validations.nthParam(1).mustBe.undefined,
  validations.nthParam(5).mustBe.object,
  validations.nthParam(7).mustBe.function,
  validations.nthParam(9).mustBe.boolean,
)(complex);
 
// This call will produce the following error
// Error: Function complex(undefined, any, any, any, object, any, function, any, boolean)
// Error: 1st parameter must be of type undefined
// Error: 5th parameter must be of type object
// Error: 7th parameter must be of type function
// Error: 9th parameter must be of type boolean
validComplex('Not Undefined');

API

export	type	params	description
validate	function	...validations: Function[]	any number of validation functions described below
validations	object		namespace object containing validations described below

---

validations

namespace	type	params	description
firstParam	object		namespace object containing validations described below
secondParam	object		namespace object containing validations described below
thirdParam	object		namespace object containing validations described below
nthParam	function	n: number	function that accepts a number and returns corresponding validations described below

---

firstParam.mustBe | secondParam.mustBe | thirdParam.mustBe | nthParam(n).mustBe

The following validation functions are provided under the above namespaces, with similar behaviour differing only in the parameter index (1-based) and the expected type.

validation name	description
string	expects a string
number	expects a number
boolean	expects a boolean
function	expects a function
object	expects an object
undefined	expects undefined

Notes

The intermediate mustBe namespace exists only to add to the fluency of the API, containing the actual validation functions.

Examples

To validate the:

1st param as string you would need:

validations.firstParam.mustBe.string

2nd param as number you would need:

validations.secondParam.mustBe.number

3rd param as boolean you would need:

validations.thirdParam.mustBe.boolean

4th param as object you would need:

validations.nthParam(4).mustBe.object

5th param as function you would need:

validations.nthParam(5).mustBe.function

6th param as undefined you would need:

validations.nthParam(6).mustBe.undefined

To use the validations you would need something like:

const func = () => {};
 
const validFunc = validate(
  validations.secondParam.mustBe.number,
  validations.nthParam(4).mustBe.object,
)(func);

License

MIT