It's method validateSchema can be imported and used as below:

const validateSchema = require('yaml-schema-validator')

// validate a json OR yml file
validateSchema('path/to/target-file.yml', {
  schemaPath: '/path/to/required/schema.yml' // can also be schema.json
})

The method automatically detects if file format is JSON or YAML and process it accordingly.

Similarly, method can also be used to validate plain JS objects:

// validate an object
let person = { name: { first: 'Tom', last: 'Xoman' }, age: 45 }
vaidateSchema(person, {
  schemaPath: '/path/to/schema.yml' // can also be schema.json
})

// validate against a JS schema object
const requiredSchema = {
  name: {
    first: { type: String, required: true },
    last: { type: String, required: true }
  },
  age: { type : Number }
}
schemaErrors = validateSchema(person, { schema: requiredSchema })

If you don't have a schema object built, but you just want to compare if structure of two objects is same, then you can use schemaObj option to pass the expected object:

let person = { name: { first: 'Tom', last: 'Xoman' }, age: 'something' }
let idealPerson = { name: { first: 'Tom', last: 'Xoman' }, age: 45 }
vaidateSchema(person, {    // compares the structure of person object against
  schemaObj: idealPerson   // anotherPerson object.
})

Schema validator validates the target file against the passed schema and lists down the mismatches in the structure:

It returns an array of errors showing the mismatches:

[{path: 'person.id', message: 'person.id must be a String'}]

Custom validators can be defined by passing an object with named validators to .use:

// custom validation function checking value for a regex
const checkHexColor = val => {
  return /^#[0-9a-fA-F]$/.test(val)
}

const car = new Schema({
  color: {
    type: String,
    use: { checkHexColor }
  }
})

Define a custom error message for the validator:

car.message({
  checkHexColor: path => `${path} must be a valid hex color.`
})

options parameter passed as the second argument in the validate schema method.

validateSchema(targetObject, options);

It has following configurable options available:

• schema: javascript object having the schema structure (eg: {name: { type: String, required: true })
• schemaPath: path to the json/yaml file having the schema
• schemaObj: Used when you directly want to compare the target with a structure of another object. Pass the expected object in this option to verify the target object is having the similar structure
• logLevel: specify the level of logging while validating schem. Possible values ['none', 'error', 'warn', 'verbose'] . By default the logLevel is set to error

• type: field that can be boolean | string | number to define type of value of that property
• required: field can be set to true if the property is required in target file
• length : feild can be used for string values to check minimum and max length of string. example length: { min: 3, max: 32 }
• use : an object of custom validation methods to be checked for a particular field. Each function in use object should take value param as input and return a boolean.

---
person:
  name:
    first_name:
      type: string
  age:
    type: number
    required: true
  employeed:
    type: boolean
  hobbies:
  - type: string

{
  "person": {
    "names": {
      "first_name": { "type": "string", "length": { "min": 3, "max": 32 } },
      "last_name": { "type": "string" }
    },
    "id": { "type": "string" },
    "age": { "type": "number", "required": true },
    "employeed": { "type": "boolean" },
    "hobbies": [{"type": "string"}],
    "attributes": [{ "foo": { "type": "string" } }]
  }
}

This package also can be used as a command line utility.

• Basic syntax: schema [command] [options]
• In root folder of your project, use command: schema validate -f path/to/dummy.yml -s path/to/schema.yml
• for help about the options use command: schema validate -h

• -f, --filePath : [Required param] path to the target file for validating
• -s, --schema [schemaPath] : path to an external schema file. If not passed the schema is fetched from /examples/schema.json which is the defeault schema location.
• -o, --schema-obj [schemaObj] : stringified JSON object whose structure you want the target object to be compared with.
• -t, --target [targetObj] : stringified JSON object whose structure is to be verified
• -j, --json : Passed if target file is in JSON format
• -e, --exit-on-err : Exit process with nonzero status on errors or warnings

• You can also make alias for the command in your package.json. Just add the script key:

"scripts": {
  "sc": "schema"
},

and then try sc validate -f path/to/dummy.yml -s path/to/schema.yml