Unable to generate ESM-compatible standalone code

[cjscheller]

The version of Ajv you are using 8.12

The environment you have the problem with node v16.16.0, ESM project ({type: module})

Your code (please make it as small as possible to reproduce the issue)

Code to compile AJV schema:

// compile.js

import Ajv from "ajv";
import standaloneCode from "ajv/dist/standalone/index.js";
import { writeFile } from "fs/promises";

const ajvOptions = {
    strict: true,
    allErrors: true,
    messages: true,
    code: {
        source: true,
        esm: true, // ESM support
    },
};

const ajv = new Ajv(ajvOptions);

const exampleSchema = {
    type: "object",
    properties: {
        body: {
            type: "object",
            properties: {
                firstName: {
                    type: "string",
                    minLength: 1,
                },
                lastName: {
                    type: "string",
                },
            },
            required: ["firstName", "lastName"],
            additionalProperties: false,
        },
    },
};

compileJsonSchema(exampleSchema);

// Note: excluded code that runs this function
async function compileJsonSchema(schema) {
    try {
        // Compile schema via AJV
        const compiled = ajv.compile(schema);

        // Build output module file content via AJV's standalone
        let moduleCode = standaloneCode(ajv, compiled);

        // Write file to parent directory of source file
        await writeFile("./schema.js", moduleCode, "utf-8");
    } catch (err) {
        console.error(err);
    }
}

Results in node.js v8+ Able to successfully compile standalone code; unable to import in ESM project

Results and error messages in your platform

I am using the standalone validation code functionality to generate compiled schema files at build time. I am compiling the code with the AJV library in a JS script and specifying esm: true to compile the standalone code for ESM. The compilation works and I am writing the compiled schema to a JS file, but I am unable to import the standalone code from this schema file in my ESM project because it imports the ucs2length utility via a require statement (const func2 = require("ajv/dist/runtime/ucs2length").default).

Here is an example schema compiled via standalone for ESM support (generated with the above script:

"use strict";export const validate = validate10;export default validate10;const schema11 = {"type":"object","properties":{"body":{"type":"object","properties":{"firstName":{"type":"string","minLength":1},"lastName":{"type":"string"}},"required":["firstName","lastName"],"additionalProperties":false}}};const func2 = require("ajv/dist/runtime/ucs2length").default;function validate10(data, {instancePath="", parentData, parentDataProperty, rootData=data}={}){let vErrors = null;let errors = 0;if(data && typeof data == "object" && !Array.isArray(data)){if(data.body !== undefined){let data0 = data.body;if(data0 && typeof data0 == "object" && !Array.isArray(data0)){if(data0.firstName === undefined){const err0 = {instancePath:instancePath+"/body",schemaPath:"#/properties/body/required",keyword:"required",params:{missingProperty: "firstName"},message:"must have required property '"+"firstName"+"'"};if(vErrors === null){vErrors = [err0];}else {vErrors.push(err0);}errors++;}if(data0.lastName === undefined){const err1 = {instancePath:instancePath+"/body",schemaPath:"#/properties/body/required",keyword:"required",params:{missingProperty: "lastName"},message:"must have required property '"+"lastName"+"'"};if(vErrors === null){vErrors = [err1];}else {vErrors.push(err1);}errors++;}for(const key0 in data0){if(!((key0 === "firstName") || (key0 === "lastName"))){const err2 = {instancePath:instancePath+"/body",schemaPath:"#/properties/body/additionalProperties",keyword:"additionalProperties",params:{additionalProperty: key0},message:"must NOT have additional properties"};if(vErrors === null){vErrors = [err2];}else {vErrors.push(err2);}errors++;}}if(data0.firstName !== undefined){let data1 = data0.firstName;if(typeof data1 === "string"){if(func2(data1) < 1){const err3 = {instancePath:instancePath+"/body/firstName",schemaPath:"#/properties/body/properties/firstName/minLength",keyword:"minLength",params:{limit: 1},message:"must NOT have fewer than 1 characters"};if(vErrors === null){vErrors = [err3];}else {vErrors.push(err3);}errors++;}}else {const err4 = {instancePath:instancePath+"/body/firstName",schemaPath:"#/properties/body/properties/firstName/type",keyword:"type",params:{type: "string"},message:"must be string"};if(vErrors === null){vErrors = [err4];}else {vErrors.push(err4);}errors++;}}if(data0.lastName !== undefined){if(typeof data0.lastName !== "string"){const err5 = {instancePath:instancePath+"/body/lastName",schemaPath:"#/properties/body/properties/lastName/type",keyword:"type",params:{type: "string"},message:"must be string"};if(vErrors === null){vErrors = [err5];}else {vErrors.push(err5);}errors++;}}}else {const err6 = {instancePath:instancePath+"/body",schemaPath:"#/properties/body/type",keyword:"type",params:{type: "object"},message:"must be object"};if(vErrors === null){vErrors = [err6];}else {vErrors.push(err6);}errors++;}}}else {const err7 = {instancePath,schemaPath:"#/type",keyword:"type",params:{type: "object"},message:"must be object"};if(vErrors === null){vErrors = [err7];}else {vErrors.push(err7);}errors++;}validate10.errors = vErrors;return errors === 0;}

I'm able to import and use the schema file by manually replacing the require with an import statement. Am I overlooking something to generate standalone validation code that is fully ESM-compatible?

[pmorch]

FYI: This is only a problem for JSON Schema generation. If I instead import Ajv from "ajv/dist/jtd.js" for JTD schemas, the code compiles fine.

[ericmorand]

Any news on this one? This is a big issue that actually prevents using AJV to generate ESM validation modules.

[Weffe]

It's not just ucs2length. I also noticed it's requiring the equal module to be used when you have a schema like this:

{ 
  "type": "string",
  "const": "my_value"
}

  const func1 = require('ajv/dist/runtime/ucs2length').default;
+ const func0 = require('ajv/dist/runtime/equal').default;

Any news on this one? This is a big issue that actually prevents using AJV to generate ESM validation modules.

@ericmorand

Our fix for now is to configure Vite to transform the standalone validation files so that CJS Require statements get modified to look like ES import syntax.

import commonjs from 'vite-plugin-commonjs';

const config = defineConfig({
    plugins: [
        commonjs({
            filter: (id) => {
                const fileRegex = /precompiled.*validations\.js$/;
                return fileRegex.test(id);
            },
        }),
    ],
    // ...

The same approach can be done for Rollup users.

[patiboh]

I solved this issue in vite using this in vite.config.js:

import commonjs from '@rollup/plugin-commonjs';

const config = {
    build: {
        rollupOptions: {
            //... other options
            plugins: [commonjs({ transformMixedEsModules: true })],
        }
    }
};

As mentioned beforehand, you could also use { transformMixedEsModules: true } in a rollup config

[hschletz]

The workaround with the "commonjs" plugin did not work for me, maybe because I don't compile the validation code to a file, but in-memory via the "virtual" plugin. I had to monkey-patch the generated code and replace the require() lines with proper imports:

import func2 from 'ajv/dist/runtime/ucs2length'
import {fullFormats} from 'ajv-formats/dist/formats'
const formats0 = fullFormats.date

Actual code may vary depending on used features. Needless to say, this is a fragile hack and no substitute for a proper fix.