const options = {
  discriminator: true,
  async loadSchema(url) {
    console.log('loadSchema', url)
    const name = url.substring("scheme://".length)
    return schemas[name]
  },
};

const schemas = {
  main: {
    type: "object",
    discriminator: {propertyName: "foo"},
    required: ["foo"],
    oneOf: [
      {
        $ref: "scheme://schema1",
      },
      {
        $ref: "scheme://schema2",
      },
    ],
  },
  schema1: {
    type: "object",
    properties: {
      foo: {const: "x"},
    },
  },
  schema2: {
    type: "object",
    properties: {
      foo: {enum: ["y", "z"]},
    },
  },
};

const Ajv = require("ajv");
const ajv = new Ajv(options);
// If you uncomment this, then there is no error
// Object.entries(schemas).forEach(([id, schema]) => {
//   ajv.addSchema(schema, 'scheme://' + id)
// })
async function main() {
  const validate = await ajv.compileAsync(schemas.main)
  validate(data)
}
main().catch((err) => console.log(err))