Skip to main content
Deno 2 is finally here 🎉️
Learn more

matches_json_schema

Version 2.0 (October 2021).

Downstream from https://gitlab.com/jane314/matches_json_schema.

About

Provides functions matches_json_schema(schema_json, obj) and matches_obj_schema(schema, obj), which return true or false: whether or not obj matches the provided schema.

Schema validation happens as follows.

There are 4 primitive types in JSON:

  • number
  • string
  • null
  • undefined and 2 complex types:
  • Array
  • Object. We also allow another type only for use by validation functions in schemas: function. In this writeup, “type” always means a primitive type or complex type, by this definition. You can forget about all other Javascript and Typescript ideas of “type” for the purposes of this library.

What matches_json_schema does is check that an object has the same type structure as a reference schema object, and (new in version 2.0!) check that certain tree nodes satisfy a validation function.

Validation is defined recursively as:

  • If schema is type function, then obj matches schema if and only if schema(obj) is true.
  • If schema and obj are both primitive types, then obj matches schema if and only if schema and obj are the same primitive type.
  • If schema and obj are both complex types, then:
    • If schema and obj are both type Array, then obj matches schema if and only if each element in the array obj matches schema schema[0].
    • If schema and obj are both type Object, then obj matches schema if and only if for each key key of schema, the object obj also has the key key, and obj[key] is of type schema[key].

So, for Arrays, we can check that every element in the Array is of a certain type. For Objects, we check that certain keys are present and associated with certain types. Extra keys are fine. And if a node in a schema is function type, we check that the corresponding node in the object passes that validation function.

Examples

import {
  matches_json_schema,
  matches_obj_schema,
} from "../matches_json_schema.js";

let schema_json = `
{
    "a": 0,
    "b": {
        "c": "",
        "d": 0,
        "e": null
    }
}
`;

// Matching Object
let obj = {
  a: 34,
  b: {
    c: "hello",
    d: 12,
    e: null,
    f: [],
  },
  c: [undefined, 4],
};

console.log(matches_json_schema(schema_json, obj)); // Prints true

// Schema
let schema = [0];

// Matching Object
obj = [2, 3, 5, 7, 11, 13];

console.log(matches_obj_schema(schema, obj)); // Prints true

// Schema
schema = {
    name: '',
    date: str => (new Date(str)).toString() !== 'Invalid Date'
}

obj = {
    name: 'Janie',
    date: 'oct 10, 2021 11:44 AM UTC-5'
};

console.log(matches_obj_schema(schema, obj)); // Prints true

Deno

Example with Deno!

import { matches_json_schema } from "https://deno.land/x/matches_json_schema/matches_json_schema.js";

console.log(matches_json_schema("null", null)); // Prints true