Build a typed library API

A distributor needs the same price calculation in its order Endpoint, invoice Job and sales preview. Put that rule in a TypeScript Library called Pricing. A change then has one implementation to review, while each caller keeps responsibility for its own permissions and writes. This example uses fictional Asterion Supply data. It has no dependency on customer code or an external service.

1. Create the Library

In Studio → Components, create a TypeScript Library named Pricing, with category commerce. The category organizes navigation; callers use the name Pricing. The platform creates a native, permanent element with the key @default. The tree displays a code icon and the lowercase italic label default. Its initial source is a documentation comment with no exports. Edit its source to define your API. You cannot rename, delete or replace that element; adding an ordinary element called DEFAULT creates a separate namespace.

What you see	What you author or call
default in the tree	Source stored under `@default`
Main exported function	`lib.Pricing.quote(...)`
Main exported type	`lib.Pricing.QuoteLine`
An ordinary `Availability` element	`lib.Pricing.Availability.canFulfil(...)`

Studio showing the lowercase default Library element and exported Pricing quote function — The real Pricing Library in the synthetic Asterion instance: the permanent default element opens as @default.

@default is a platform element identity. It does not enable the JavaScript syntax export default.

2. Define the price contract

Replace the default’s comment with this source. Money uses integer minor units; discounts use basis points (750 means 7.5%). The policy here rounds each line after discount, then sums the lines. State your own accounting policy explicitly before using this in a real invoice system.

Pricing · @default

export interface QuoteLine {
  sku: string;
  quantity: number;
  unitPriceMinor: number;
  discountBps: number;
}

export interface Quote {
  totalMinor: number;
  lines: { sku: string; netMinor: number }[];
}

function integer(value: number, minimum: number, maximum: number): void {
  if (!Number.isSafeInteger(value) || value < minimum || value > maximum) {
    throw new Error('Invalid price input');
  }
}

/** Calculate a quote without changing inventory or creating an invoice. */
export function quote(input: QuoteLine[]): Quote {
  if (input.length === 0 || input.length > 500) throw new Error('Use 1–500 lines');
  const lines = input.map(line => {
    integer(line.quantity, 1, 100000);
    integer(line.unitPriceMinor, 0, 100000000);
    integer(line.discountBps, 0, 10000);
    const weighted = line.quantity * line.unitPriceMinor * (10000 - line.discountBps);
    if (!Number.isSafeInteger(weighted)) throw new Error('Price exceeds supported precision');
    return { sku: line.sku, netMinor: Math.round(weighted / 10000) };
  });
  const totalMinor = lines.reduce((sum, line) => sum + line.netMinor, 0);
  if (!Number.isSafeInteger(totalMinor)) throw new Error('Quote exceeds supported precision');
  return { totalMinor, lines };
}

The integer helper stays local. JSDoc describes the exported function for callers; annotations such as @public or @private do not change visibility. Actual named export statements define the API.

3. Inspect completion in Monaco

Save and activate the Library through your normal deployment review. Open a consuming TypeScript Component in the same instance. Type each expression below and invoke completion with Ctrl+Space if it does not open automatically.

Typed text	Expected public contract
`lib.`	Accessible active Library names, including `Pricing`
`lib.Pricing.`	`quote` and exported type declarations in the appropriate TypeScript context
`lib.Pricing.quote(`	Parameter and return-type help with the function’s documentation
`lib.Pricing.integer`	No public helper with that name

Monaco completion after lib.Pricing. suggests the exported quote function — Completion in a consuming TypeScript Component exposes quote; the unexported integer helper remains private.

Declare a typed input to see field suggestions:

Order preview · Main

const lines: lib.Pricing.QuoteLine[] = [
  { sku: 'AST-FILTER-100', quantity: 4, unitPriceMinor: 1250, discountBps: 750 },
];
return lib.Pricing.quote(lines);

Expected output:

{
  "totalMinor": 4625,
  "lines": [{ "sku": "AST-FILTER-100", "netMinor": 4625 }]
}

Definition navigation takes you to the owning Library element. The short namespace is also the TypeScript type namespace: use lib.Pricing.QuoteLine, rather than attempting to use @default as a TypeScript namespace identifier. Types have no JavaScript runtime value.

4. Add a named capability

Add an ordinary element named Availability:

Pricing · Availability

export function canFulfil(available: number, requested: number): boolean {
  return Number.isSafeInteger(requested) && requested > 0 && available >= requested;
}

Call it as lib.Pricing.Availability.canFulfil(12, 4). The default does not automatically forward its members. Avoid naming a default export Availability: default export names, including type names, cannot collide with element keys. Check a no-discount line, a full-discount line, a fractional quantity, an empty input and an amount beyond supported precision. Test the caller as well: a correct quote does not reserve stock, authorize a buyer or make a write idempotent. For a missing completion, check the exact case-sensitive Library name, its active status, explicit exports and current editor diagnostics. Refresh a CLI or VS Code workspace from the canonical source after an upgrade before submitting old source. Continue with Library lifecycle and restrictions, debugging and the enterprise example.

Build applications

Low-code runtime

Low-code reference

Build a typed library API

1. Create the Library

2. Define the price contract

3. Inspect completion in Monaco

4. Add a named capability

​1. Create the Library

​2. Define the price contract

​3. Inspect completion in Monaco

​4. Add a named capability

​5. Validate before sharing the rule

1. Create the Library

2. Define the price contract

3. Inspect completion in Monaco

4. Add a named capability

5. Validate before sharing the rule