Quick Start

A simple schema


import { SchemaBuilder } from "@jetio/schema-builder";
 
const userSchema = new SchemaBuilder()
  .object()
  .properties({
    name: (s) => s.string().minLength(2),
    age: (s) => s.number().minimum(18),
  })
  .required(["name", "age"])
  .build();

That produces exactly this JSON Schema:


{
  "type": "object",
  "properties": {
    "name": { "type": "string", "minLength": 2 },
    "age": { "type": "number", "minimum": 18 }
  },
  "required": ["name", "age"]
}

Builder, type, and validator together

This is the whole pitch in one example — a single schema produces the JSON Schema, a TypeScript type, and a compiled validator, all enforcing the same rules.


import { SchemaBuilder, Jet, JetValidator } from "@jetio/schema-builder";
 
const accountSchema = new SchemaBuilder()
  .object()
  .properties({
    accountType: (s) => s.string(),
    username: (s) => s.string(),
    companyName: (s) => s.string(),
    email: (s) => s.string().format("email"),
  })
  .required(["accountType", "email"])
  .if((s) =>
    s.object().properties({
      accountType: (s) => s.const("personal"),
    }),
  )
  .then((s) => s.object().required(["username"]))
  .elseIf((s) =>
    s.object().properties({
      accountType: (s) => s.const("business"),
    }),
  )
  .then((s) => s.object().required(["companyName"]))
  .end()
  .build();
 
// 1. Type inference
type Account = Jet.Infer<typeof accountSchema>;
// personal → username required | business → companyName required | base otherwise
 
// 2. Runtime validation
const validator = new JetValidator({ allErrors: true });
const validate = validator.compile(accountSchema);
 
validate({
  accountType: "personal",
  email: "alice@example.com",
  username: "alice",
}); // true
 
validate({
  accountType: "personal",
  email: "alice@example.com",
  // missing username!
}); // false
 
console.log(validate.errors);
// [{ dataPath: '/', keyword: 'required', message: "must have required property 'username'" }]

The conditional above uses the elseIf extension for clean chaining. See Conditionals for the full builder API and Type Inference → Conditionals for how the type is derived.

Next steps

Learn the full builder API in the Guide.
Understand how types are derived in Type Inference.
Browse complete, real-world schemas in Examples.