Webpack loader that compiles JSON strings into Ajv validation functions using ajv-pack

ajv, webpack, loader, json, schema, validation, precompile
npm install ajv-json-loader@0.1.4



Build Status

Webpack loader that compiles JSON strings into Ajv validation functions using ajv-pack

Slightly increases application performance - all schemas are compiled at build step, not at runtime

It also decreases build size because of excluding Ajv library itself from bundle

However, it may depend on total size of schemas. For few schemas with small size it's a 100% profit. Not sure about the ratio between size of JSON-schema and size of compiled function, so for large schemas it may be not so useful


npm i -D ajv-json-loader


Use it as loader for JSON-schemas in your webpack config like this:

module.exports = {
  // ...
  module: {
    loaders: [
        test: /\.schema\.json$/,
        use: [
            loader: 'ajv-json-loader',
            options: {
              ajv: {
                // Pass any Ajv constructor options here
                allErrors: true,
        // "type" option only for Webpack >= 4
        // (https://webpack.js.org/configuration/module/#ruletype)
        type: "javascript/auto"

Then you can use your schemas like this:

const validateMySchema = require('/path/to/schemas/my.schema.json');

if (validateMySchema(data)) {
} else {
  console.error('Invalid: ' + validateMySchema.errors.join(','));

Referencing to external schemas (using $ref)

Loader uses Ajv's loadSchema option to load external schemas. Default implementation will try to just require file with name specified in $ref field to load referenced schema. You can override it by passing corresponding option to loader (see example above)

If you think that your custom loadSchema option is pretty general, feel free to create an issue or PR to add it as loader option to make webpack config more clean

For example, if you have following schemas in /path/to/schemas:


  "id": "foo.json#",
  "properties": {
    "bar": { "$ref": "bar.json#/definitions/bar" }


  "id": "bar.json#",
  "properties": {
    "baz": {
      "type": "string"

Loader will call require(path.resolve('/path/to/schemas', 'bar.json')) to load bar.json# schema

TypeScript typings

If you are using TypeScript, you can add typings to your project like this:

declare module '*.schema.json' {
  import { ErrorObject } from 'ajv';

  interface ValidateFn {
      (data: object): boolean;
      errors: ErrorObject[] | null;
  const validate: ValidateFn;
  export default validate;

Then when you import your schema After this TypeScript compiler will know that modules ending with .schema.json exports an ValidateFn object


This loader uses ajv-pack package, so limitations are the same