data-type-check-js v1.0.3

data-type-check-js

A simple data type checks in Javascript.

Introduction

To check what data type something has in javascript is not always the easiest. The language itself provides an operator called typeof for that which works in a straightforward way. Typeof returns a string of what a values data type is, so for an object "object" is returned and for a string "string".

Installation

Run

npm install data-type-check-js

Example

const typecheck = require('data-type-check-js');

// isString()
const isStringTrue = typecheck.isString('hello');
// isStringTrue === true -> true

// isString()
const isStringFalse = typecheck.isString(123);
// isStringFalse === true -> false

Usage

const typecheck = require('data-type-check-js');

/**
 * Returns true if a value is a string.
 * A string is always a string so this one is easy.
 * Except if called with new (new String) typeof will instead return "object".
 * So to also include those strings instanceof can be used.
 */
typecheck.isString(value);

/**
 * Returns true if a value is really a number.
 * From typeof more things than just an ordinary number will return "number" like NaN and Infinity.
 * To know if a value really is a number the function isFinite is also required.
 */
typecheck.isNumber(value);

/**
 * Returns true if a value is an array.
 * In javascript arrays are not true arrays like in java and in other languages.
 * They're actually objects so typeof will return "object" for them.
 * To know if something's really an array its constructor can be compared to Array.
 */
typecheck.isArray(value);

/**
 * Returns true if a value is a function.
 * Functions are functions so here just typeof is enough.
 */
typecheck.isFunction(value);

/**
 * Returns true if a value is an object.
 * Many things are objects in javascript.
 * To know if a value is an object that can have properties and be looped through,
 * its constructor can be compared to Object. It doesn't work for objects created from classes,
 * then the instanceof operator can be used instead.
 */
typecheck.isObject(value);

/**
 * Returns true if a value is null.
 * Most times you don't need to check explicitly for null and
 * undefined since they're both falsy values.
 * However to do it below functions does the trick.
 */
typecheck.isNull(value);

/**
 * Returns true if a value is undefined.
 * Most times you don't need to check explicitly for null
 * and undefined since they're both falsy values.
 */
typecheck.isUndefined(value);

/**
 * Returns true if a value is a boolean.
 * For booleans typeof is enough since it returns "boolean" for both true and false.
 */
typecheck.isBoolean(value);

/**
 * Returns true if a value is a regexp.
 * RegExp's are objects so the only thing needed to check is if the constructor is RegExp.
 */
typecheck.isRegExp(value);

/**
 * Returns true if value is an error object.
 * Errors in javascript are the same as "exceptions" in many other programming languages.
 * They come in a couple different forms like for instance Error, TypeError and RangeError.
 * An instanceof statement is enough for them all,
 * but just to be extra sure we also check for the "message" property that errors have.
 */
typecheck.isError(value);

/**
 * Returns true if value is a date object.
 * Date isn't really a data type in javascript.
 * But to know if something's a Date object it can be checked with instanceof.
 */
typecheck.isDate(value);

/**
 * Returns true if a Symbol.
 * In ES6 the new datatype Symbol was added.
 * Nicely enough typeof returns "symbol" for it so no more logic is required.
 */
typecheck.isSymbol(value);

Tests

npm run test-coverage

> @gwennhester/type-check-js@1.0.0 test-coverage /Users/gwenn/Projects/Packages/type-check-js
> jest --coverage --verbose

 PASS  __tests__/index.test.js
  isString()
    ✓ it should return true if given a valid string (1 ms)
    ✓ it should return false if given an invalid string
  isNumber()
    ✓ it should return true if given a valid number
    ✓ it should return true if given an invalid number
  isArray()
    ✓ it should return true if given an array
    ✓ it should return false if given an invalid array (1 ms)
  isFunction()
    ✓ it should return true if given a function
    ✓ it should return false if given an invalid function
  isObject()
    ✓ it should return true if given an object
    ✓ it should return false if given an invalid object (1 ms)
  isNull()
    ✓ it should return true if given a null value
    ✓ it should return false if given a non null value
  isUndefined()
    ✓ it should return true if given an undefined value
    ✓ it should return false if given a non undefined value (1 ms)
  isBoolean()
    ✓ it should return true if given a boolean value
    ✓ it should return false if given a non boolean value
  isRegExp()
    ✓ it should return true if given a regexp value
    ✓ it should return false if given a non regexp value (1 ms)
  isError()
    ✓ it should return true if given an error value
    ✓ it should return false if given a non error value
  isDate()
    ✓ it should return true if given a date value
    ✓ it should return false if given a non date value (1 ms)
  isSymbol()
    ✓ it should return true if given a symbol value
    ✓ it should return false if given a non symbol value

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |
 index.js |     100 |      100 |     100 |     100 |
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       24 passed, 24 total
Snapshots:   0 total
Time:        0.233 s, estimated 1 s
Ran all test suites.

Reference

https://webbjocke.com/javascript-check-data-types/