0.0.3 • Public • Published

A simple tool for validation and type checking of variables in JavaScript


Validator is available through the npm registry:

$ npm install @oneisland/validator


After installing Validator you can use the module like so:

// Import the the validator module
import { Validator } from '@oneisland/validator';

// Describe the Validator for the class
const { validate } = new Validator('Simple');

// Create a simple class
class Simple {

  // Create an instance from two numbers
  constructor(a, b) {

    // Check that 'a' and 'b' are numbers
    validate({ a, b }, 'Number');

    // Check that 'a' is an odd number
    validate({ a }, (v) => (v % 2), `"a" to be an odd number`);

    // Check that 'b' is an even number
    validate({ b }, (v) => !(v % 2), `"b" to be an even number`);

    // Bind the values
    this.values = [a, b];

// Create a simple function
const caseA = new Simple(1, 2);

// Log out a message with the data
console.log('Values (Case A):', caseA.values);

// Create a simple function (throws an error and terminates the application)
const caseB = new Simple(2, true);

// Log out a message with the data (this line will never be reached)
console.log('Values (Case B):', caseB.values);

Running the following code with Node:

$ node simple-example.js

The script will something similar to the following, terminating before logging Case B:

Values (Case A): [ 1, 2 ]

TypeError: new Simple expects "b" to be a Number

Please read the documentation below for more details on how to configure Validator.

You can also check out our tests or the source code of our Mesh library for more complex usage.



class Validator {

  constructor(name) {}

  validate(variables, validation, description?) {}

  validateArray(variables, validation, description?) {}

Validator is a class which is instantiated for usage within a Class or Object.

Once instantiated, a validator exposes two functions for use:

  • validate - Validate that one or more variables meet a condition and throw an error if not
  • validateArray - Validate each value of one or more array variables using the validate function



The name parameter defines the name of the caller which the validator runs inside.

The name should be a String.

The name should be name of the Class or Object which contains the method of property which calls this Validator.

// Example (for the class Polygon)


The validate function accepts an Object of variables which it will check against the validated against the validation conditions.

The validate function can also accepts a description which defines what is expected of the validation function.

// Example usage (check type or species)
validate({ text }, 'String');
validate({ a, b, c }, 'Point');

// Example usage (check one of type of species)
validate({ triangle }, ['Face', 'Polygon']);

// Example usage (check with function)
validate({ score }, (score) => (score.teamA != score.teamB));

Check out the tests for more usage examples.


The variables parameter defines which variables are to be validated.

The variables should be an Object of one or more variables which should be validated.

The variables can be of any type, and can contain a property species which can be used to check the type of a variable.

// Example usage (three points in a triangle)
{ a, b, c }

The validation parameter defines how to validate the variables.

The validation should be one of following types:

  • A String:

    • The validation defines a type (e.g. Number) or a species (e.g. Polygon).

    • This is used to check that each variable is has the type of validation or contains a property species which is equal to the validation.

      // Examples (primative data types):
      // Examples (species types)
  • An Array of Strings:

    • The validation defines an Array of types (e.g. Number) or a species (e.g. Polygon)

    • This is used to check that each variable has one of the types or species as defined validation.

      // Examples (primative data types and species types)
      ['String', 'Word']
      ['Vertex', 'Point']
  • A Function:

    • The validation defines a function to check each of the variables against.

    • The validation function will pass the paramaters value (the value of the variable) and index (the index within an Array when called from validateArray).

    • This function will be used to check that each variable.

      // Example (check value of variable is less than 10)
      (value) => (value < 10);
      // Example (check that the variable has no children)
      (value) => (value.children.length == 0);
      // Example (check the value is not the same as the next one)
      (value, index) => (value != values[((index + 1) % values.length)]);

The description is an optional paramater which defines the expectation of the validation.

The description should be a String.

The description will be be added to the error message if the validation fails.

// Example (for an Array of Point)
`"points" to be an array of Point`


The validateArray function accepts the same paramater options as the validate function but expects each of the variables to be an Array.

The validateArray function will check that each value within each of the variables meets the validation conditions.

// Example usage (check type or species)
validateArray({ words }, 'String');
validateArray({ points }, 'Point');

// Example usage (check one of type of species)
validateArray({ triangles }, ['Face', 'Polygon']);

// Example usage (check with function)
validateArray({ teams }, (team) => (team.members =< 5 && team.members < 8));
validateArray({ ordered }, (number, i) => ((i < 0) ? number > ordered[i - 1] : true));

Check out the tests for more usage examples.



Copyright (c) 2019-present, OneIsland Limited

Package Sidebar


npm i @oneisland/validator

Weekly Downloads






Unpacked Size

27.7 kB

Total Files


Last publish


  • danzlarkin