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feat: enable Ajv2019 and Ajv2020 #152

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b93e6e7
feat: allow Ajv 2019/2020
jmjf Jun 7, 2025
8ec175b
feat(docs): update README
jmjf Jun 7, 2025
6ea7611
Change README per code review feedback
jmjf Aug 16, 2025
965aed3
Merge branch 'main' into feat-enable-2019-2020
gurgunday Aug 17, 2025
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14 changes: 14 additions & 0 deletions README.md
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Expand Up @@ -79,6 +79,20 @@ const app = fastify({
})
```

### Fastify with Ajv2019 or Ajv2020

If you want to use Ajv2019 or Ajv2020 for newer JSON Schema features, you can do it be passing the `ajv.mode` option.

```js
const app = fastify({
ajv: {
mode: '2019' // or '2020'
}
})

// app uses Ajv2019 for validation
```

### Fastify with JTD

The [JSON Type Definition](https://jsontypedef.com/) feature is supported by AJV v8.x and you can benefit from it in your Fastify application.
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11 changes: 3 additions & 8 deletions lib/validator-compiler.js
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@@ -1,19 +1,14 @@
'use strict'

const Ajv = require('ajv').default
const AjvJTD = require('ajv/dist/jtd')

const defaultAjvOptions = require('./default-ajv-options')

class ValidatorCompiler {
constructor (externalSchemas, options) {
// This instance of Ajv is private
// it should not be customized or used
if (options.mode === 'JTD') {
this.ajv = new AjvJTD(Object.assign({}, defaultAjvOptions, options.customOptions))
} else {
this.ajv = new Ajv(Object.assign({}, defaultAjvOptions, options.customOptions))
}
const ajvPath = ['JTD', '2019', '2020'].includes(options.mode) ? `ajv/dist/${options.mode.toLowerCase()}` : 'ajv'
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@Eomm Eomm Aug 15, 2025

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I would refactor a bit here, because it is strange to me that we don't support the default version.

I would implement something like:

const supportedModes = new Map()

supportedModes.add('2020', () => require('ajv/dist/2020'))
supportedModes.add('2019', () => require('ajv/dist/2019'))
supportedModes.add('draft-04', () => require('ajv/dist/refs/json-schema-draft-06.json'))

const Ajv = require(ajvPath)
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@climba03003 climba03003 Jun 7, 2025

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It doesn't look like same as before. Previously, accessing the .default.

Suggested change
const Ajv = require(ajvPath)
const Ajv = require(ajvPath)

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@jmjf jmjf Jun 8, 2025

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This allows using Ajv2019 and Ajv2020 by passing 2019 or 2020 in options.mode.

If options.mode is not one of JTD, 2019, or 2020, ajvPath is "ajv" (the default).

If I'm misunderstanding the question, please help me understand.

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@climba03003 climba03003 Jun 8, 2025 •
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I means const Ajv = require('ajv').default, now becomes const Ajv = require('ajv')
Unsure why the .default exist.

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@jmjf jmjf Jun 8, 2025 •
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I see. Thanks for explaining. This became a learning opportunity for me.

What I learned is, Ajv is ESM. According to Node docs

When an ES Module contains both named exports and a default export, the result returned by require() is the module namespace object, which places the default export in the .default property, similar to the results returned by import(). To customize what should be returned by require(esm) directly, the ES Module can export the desired value using the string name "module.exports".

In Ajv code, Ajv uses module.exports, so require('ajv') should get the Ajv class, which is the default export. The JTD, 2019, and 2020 versions do the same.

My guess is that, in the past, require().default may have been required to get the default export out of the module namespace object. The JTD code wasn't using .default and worked and this code works without .default.

I don't mind adding a commit to add the .default if wanted.

This morning, I woke up thinking I should typeof options.mode === 'string' to the ternary condition to avoid trying to call toLowerCase on a non-string (would default to plain Ajv if options.mode is not a string or is not one of the three recognized options).

But Array.prototype.includes doesn't coerce types, so non-string won't match and won't attempt to call toLowerCase, so not needed. (Another thing I learned.)

this.ajv = new Ajv(Object.assign({}, defaultAjvOptions, options.customOptions))

let addFormatPlugin = true
if (options.plugins && options.plugins.length > 0) {
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32 changes: 18 additions & 14 deletions test/duplicated-id-compile.test.js
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Expand Up @@ -37,19 +37,23 @@ const fastifyAjvOptionsDefault = Object.freeze({
customOptions: {}
})

test('must not store schema on compile', t => {
t.plan(5)
const factory = AjvCompiler()
const compiler = factory({}, fastifyAjvOptionsDefault)
const postFn = compiler({ schema: postSchema })
const patchFn = compiler({ schema: patchSchema })
for (const mode of [undefined, '2019', '2020']) {
test(`mode: ${mode ?? 'default'}`, async (t) => {
await t.test('must not store schema on compile', t => {
t.plan(5)
const factory = AjvCompiler()
const compiler = factory({}, fastifyAjvOptionsDefault)
const postFn = compiler({ schema: postSchema })
const patchFn = compiler({ schema: patchSchema })

const resultForPost = postFn({})
t.assert.deepStrictEqual(resultForPost, false)
t.assert.deepStrictEqual(postFn.errors[0].keyword, 'required')
t.assert.deepStrictEqual(postFn.errors[0].message, "must have required property 'username'")
const resultForPost = postFn({})
t.assert.deepStrictEqual(resultForPost, false)
t.assert.deepStrictEqual(postFn.errors[0].keyword, 'required')
t.assert.deepStrictEqual(postFn.errors[0].message, "must have required property 'username'")

const resultForPatch = patchFn({})
t.assert.ok(resultForPatch)
t.assert.ok(!patchFn.errors)
})
const resultForPatch = patchFn({})
t.assert.ok(resultForPatch)
t.assert.ok(!patchFn.errors)
})
})
}
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