#Custom chain methods

Last updated: 2026-06-18

Use this page when you want to add a method to an existing builder:

s('string!').tenantId().label('Tenant')

This is different from a custom DSL type and different from an s.xxx() factory.

#Add the runtime builder method

registerExtension() can register a DSL literal and a namespace factory, but it does not automatically add a method to DslBuilder.prototype. Provide the runtime method in your extension setup:

import { DslBuilder, type IDslBuilder } from 'schema-dsl/pure';

export function installTenantIdChainMethod() {
  const proto = DslBuilder.prototype as unknown as {
    tenantId?: (this: IDslBuilder) => IDslBuilder;
  };

  proto.tenantId ??= function tenantId(this: IDslBuilder) {
    return this.pattern(/^tenant_[a-z0-9]+$/);
  };
}

The method should be idempotent so hot reload, repeated test setup, or plugin reinstall does not keep replacing it.

#Add TypeScript builder hints

import type { IDslBuilder } from 'schema-dsl/pure';

declare module 'schema-dsl/pure' {
  interface IDslBuilder {
    tenantId(): this;
  }
}

Now s('string!').tenantId() has builder method hints.

#Add direct String-chain hints

Only add this when your project explicitly uses direct String-chain source code:

import 'schema-dsl/string-types';
import type { IDslBuilder } from 'schema-dsl/pure';

declare module 'schema-dsl/string-types' {
  interface SchemaDslStringExtensions {
    tenantId(): IDslBuilder;
  }
}

Direct String-chain code still needs one of these runtime paths:

• compile-time transform with schema-dsl/transform or schema-dsl/esbuild;
• explicit String extension installation through schema-dsl/register-string;
• the compatibility/root entry when you intentionally accept the v1 String extension behavior.

#Configure transform for custom methods

When transforming direct String-chain source, add the method name:

import { transformSchemaDsl } from 'schema-dsl/transform';

const result = transformSchemaDsl(
  'export const tenant = "string!".tenantId().label("Tenant")',
  {
    filename: 'schema.ts',
    additionalMethods: ['tenantId']
  }
);

When the chain starts from a custom DSL literal, also allow that literal:

transformSchemaDsl(
  'export const tenant = "tenant-id!".tenantId()',
  {
    filename: 'schema.ts',
    additionalMethods: ['tenantId'],
    additionalTypes: ['tenant-id']
  }
);

#Recommended package shape

For reusable extensions, keep runtime implementation and type declarations together:

src/schema-dsl/
  chain-methods.ts
  chain-methods.d.ts
  transform.ts

The implementation installs the builder method. The declaration file augments schema-dsl/pure and, only when needed, schema-dsl/string-types. The transform config exports additionalMethods and additionalTypes for your build tool.

#Corresponding sample file

Example entry: custom-chain-methods.ts Note: Installs a custom builder method, validates the builder path, and verifies transform configuration for direct String-chain source.