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2.7.2 • Public • Published

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Runtime validation and processing of JavaScript types

  • Respects language nature and acknowledges its quirks
  • Allows coercion in restricted forms (rejects clearly invalid input, normalizes permissible type deviations)
  • No transpilation implied, written to work in all ECMAScript 3+ engines

Use case

Validate arguments input in public API endpoints.

For validation of more sophisticated input structures (as deeply nested configuration objects) it's recommended to consider more powerful schema based utlities (as AJV or @hapi/joi)

Example usage

Bulletproof input arguments normalization and validation:

const ensureString        = require('type/string/ensure')
    , ensureDate          = require('type/date/ensure')
    , ensureNaturalNumber = require('type/natural-number/ensure')
    , isObject            = require('type/object/is');

module.exports = (path, options = { min: 0 }) {
  path = ensureString(path, { errorMessage: "%v is not a path" });
  if (!isObject(options)) options = {};
  const min = ensureNaturalNumber(options.min, { default: 0 })
      , max = ensureNaturalNumber(options.max, { isOptional: true })
      , startTime = ensureDate(options.startTime, { isOptional: true });

  // ...logic


npm install type


Aside of general ensure validation util, following kind of utilities for recognized JavaScript types are provided:


Restricted coercion into primitive type. Returns coerced value or null if value is not coercible per rules.


Object type/kind confirmation, returns either true or false.


Value validation. Returns input value (in primitive cases possibly coerced) or if value doesn't meet the constraints throws TypeError .

Each */ensure utility, accepts following options (eventually passed with second argument):

  • isOptional - Makes null or undefined accepted as valid value. In such case instead of TypeError being thrown, null is returned.
  • default - A value to be returned if null or undefined is passed as an input value.
  • errorMessage - Custom error message. Following placeholders can be used:
    • %v - To be replaced with short string representation of invalid value
    • %n - To be replaced with meaninfgul name (to be passed with name option) of validated value. Not effective if name option is not present
  • errorCode - Eventual error code to be exposed on .code error property
  • name - Meaningful name for validated value, to be used in error message, assuming it contains %n placeholder
  • Error - Alternative error constructor to be used (defaults to TypeError)


General utils:

Type specific utils:


$ npm test



npm i type

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  • medikoo