Runtime Semantics

Values

Use normal JavaScript values:

const id = 42
const name = 'Ada'
const enabled = true
const missing = undefined

Nullish checks, booleans, strings, numbers, and object references follow JavaScript semantics.

Objects and arrays

Objects and arrays work for ordinary data handling:

const user = { id: 42, name: 'Ada' }
const names = users.map((user) => user.name)
const keys = Object.keys(user)

Computed property names are fine when the property names are ordinary runtime values:

const header = 'content-type'
headers[header] = 'application/json'

Functions

Functions, callbacks, closures, and methods are supported:

const normalize = (value: string) => value.trim().toLowerCase()
items.map((item) => normalize(item.name))

Avoid constructing functions from strings. Prefer explicit imports and named functions.

Errors

Throw and catch errors normally:

try {
  await loadConfig()
} catch (error) {
  console.error('failed to load config', error)
  throw error
}

Enable source maps when you need production stack traces to point back to source files.

What to test

Test behavior at the application boundary:

• Request and response handling.
• Error paths.
• Timers and async flows.
• Dependency adapters.
• Environment configuration.