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Simple Run-Time Type Checker
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README.md

srttc

A Simple Run-Time Type Checker for Javacript

No dependencies, no fuss.

Usage

import srttc from 'srttc';

srttc(valueToCheck, definition);

any

A special string any can be passed to match any type (including null/undefined)

const matches = srttc(5, 'any');
const matches = srttc('a value to compare', 'any');
const matches = srttc(true, 'any');
const matches = srttc({}, 'any');
const matches = srttc(new Error(), 'any');
const matches = srttc([1, 'blah'], 'any');
const matches = srttc(null, 'any');

Primitives

JS Primitive values are defined by their typeof string

const matches = srttc(5, 'number');
const matches = srttc('a value to compare', 'string');
const matches = srttc(true, 'boolean');

A square bracket pair ([]) can be used to quickly note arrays of primitive types

const matches = srttc(['value 1', 'value 2'], 'string[]');

This can be suffixed with a question mark (?) to mark it as optional

const matches = srttc(undefined, 'string?');

Objects

instanceof

Whether a value is an instance of a class can be checked by passing the constructor function of the class

const matches = srttc(new CoolObject(), CoolObject);

Property comparison

All properties on the definition must be present, but extra properties on the value are ignored

const matches = srttc(
  {
    foo: 5,
    bar: 'a string',
  },
  {
    foo: 'number',
  },
);

Properties of objects can be primitives (like above) or other objects

const matches = srttc(
  {
    foo: 5,
    bar: {
      baz: [
        new CoolObject(),
        new CoolObject(),
      ],
      quz: {
        quux: 'some weird string',
      },
    },
  },
  {
    foo: 'number',
    bar: {
      baz: srttc.arrayOf(CoolObject),
      quz: {
        quux: 'string',
      },
    },
  },
);

Arrays

Primitive arrays

See the section on primitives

Arrays of more complex types

See the section on the srttc.arrayOf() function

Typed arrays of known length (tuples)

Sometimes arrays have different types based on the position in the array

const matches = srttc([5, 'a string'], ['number', 'string']);

Optional types at the end of the array are supported

const matches = srttc([5, 'a string'], ['number', 'string', srttc.optional('boolean')]);

Extra functions

srttc.oneOf()

Also available as srttc.or() and srttc.union()

The value must match at least one of the given types for it to be valid

const matches = srttc(5, srttc.oneOf('string', 'number'));
const matches = srttc('a string', srttc.oneOf('string', 'number'));

srttc.optional()

The given type, but also matches on null or undefined.

const matches = srttc('a string', srttc.optional('string'));
const matches = srttc(undefined, srttc.optional('string'));
const matches = srttc('a string', srttc.optional(srttc.oneOf('string', 'number')));
const matches = srttc(5, srttc.optional(srttc.oneOf('string', 'number')));
const matches = srttc(null, srttc.optional(srttc.oneOf('string', 'number')));

srttc.arrayOf()

The value must be an array, and each value in the array must match the given type

const matches = srttc(['value 1', 'value 2'], srttc.arrayOf('string'));
const matches = srttc([['value 1'], ['value 2']], srttc.arrayOf(srttc.arrayOf('string')));

You can also specify a minimum and maximum length for the array

const matches = srttc(['value 1', 'value 2'], srttc.arrayOf('string', 0, Infinity));
const matches = srttc(['value 1', 'value 2'], srttc.arrayOf('string', 0, 2));
const matches = srttc(['value 1', 'value 2'], srttc.arrayOf('string', 2, 2));
const matches = srttc(['value 1', 'value 2'], srttc.arrayOf('string', 2, Infinity));

Tests

To run the unit tests, just run npm test. The tests are defined in tests/index.js

TODO

Contributions are welcome. Just fork, do a thing, then create a PR.

  • Allow OR comparisons (e.g. string or number)
  • Object (incl. constructor comparison)
  • Error mode (throws error explaining problem instead of returning false)
  • More tests?
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