Takes an array of json schemas and returns an object with middleware to validate requests

create-koa-ajv.js

const Ajv = require('ajv');

function errFormat(obj) {
    return ({ dataPath, message }) =>
        `Type Error: '${obj.schema.title}${dataPath}' ${message}.\n`;
}

function validator(ajvOptions = {}) {
    return (acc, schema) =>
        Object.assign(acc, {
            [schema.title]: (ctx, next) => {
                const ajv = new Ajv(ajvOptions);
                const validate = ajv.compile(schema);
                const valid = validate(ctx.request.body);

                if (!valid) {
                    const msg = errFormat(validate);
                    ctx.throw(400, 'validation error', msg);
                }

                next();
            }
        });
}

module.exports = ajvOptions => schemas =>
    schemas.reduce(validator(ajvOptions), {});