JSON Schema Validatior

json-schema-validator.js

const rootSchema = {
  $schema: "http://json-schema.org/draft-04/schema#",
  title: "Person",
  description: "A person",
  type: "object",
  properties: {
    name: {
      description: "A person's name",
      type: "string",
    },
    age: {
      description: "A person's age",
      type: "number",
      minimum: 18,
      maximum: 64,
    },
    location: {
      description: "Geo-coordinates of a person",
      type: "object",
    },
    friends: {
      description: "People should have some friends",
      type: "array:person",
    },
  },
  required: ["name", "age"],
};

const person = {
  name: "Jay",
  age: 77,
  friends: ["ewq", "cds"],
  location: {},
  // bob: true,
};

function validate(schema, model) {
  const schemaKeys = [...Object.keys(schema.properties)];
  const modelKeys = [...Object.keys(model)];

  for (let requiredField of schema.required) {
    if (!model[requiredField]) {
      return `Missing required property ${requiredField}`;
    }
  }

  const unexpectedProperties = modelKeys.filter(
    (key) => !schemaKeys.includes(key)
  );

  if (unexpectedProperties.length > 0) {
    return `Error, unexpected property ${unexpectedProperties} is not allowed based on schema`;
  }

  for (let key of schemaKeys) {
    if (model[key] === undefined) {
      continue;
    }

    const schemaType = schema.properties[key].type;
    const modelType = Array.isArray(model[key]) ? "array" : typeof model[key];

    if (!schemaType.includes(modelType)) {
      return `Error, property ${key} is expected to be of type ${schemaType}`;
    }
  }

  return `Your model is valid based on the schema, hurray!`;
}

console.log("|----------------------------->\n");
console.log(validate(rootSchema, person), "\n");
console.log("|----------------------------->\n");