Stack & Forbidden Constructs

Specification > Engineering

This chapter fixes the runtime, module system, and project layout for JavaScript code, and names the language constructs you must not use. It is conditional: it applies to source files written as ES modules (**/*.mjs) and does not constrain other ecosystems.

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Runtime & Modules

Aspect	Rule
Runtime	You MUST target Node.js 22 and MAY use its current syntax.
Module system	You MUST write ES modules; source files MUST use the .mjs extension.
Imports	You MUST use import / export; you MUST NOT use CommonJS require.

Project Layout

You MUST place application modules under ./src/. Runtime configuration MUST live in a single module at ./src/data/config.mjs, so that settings have one well-known location instead of being scattered across the tree.

./src/
    ./src/data/config.mjs
    ...feature modules

Forbidden Constructs

The following constructs are prohibited. Each row states the rule and the sanctioned alternative.

Construct	Rule	Use instead
for / while loops	MUST NOT	array methods (map, filter, reduce, forEach)
process.argv	MUST NOT	a dedicated configuration module
fs for risky operations	MUST NOT	guarded, purpose-built helpers
eval()	MUST NOT	explicit parsing or a lookup table
.then().catch() chains	SHOULD NOT	async / await

Iteration MUST be expressed with array methods rather than imperative loops:

// Prohibited
for( let i = 0; i < items.length; i++ ) {
    total += items[ i ].price
}

// Required
const total = items.reduce( ( sum, item ) => sum + item.price, 0 )

Asynchronous Control Flow

You SHOULD express asynchronous work with async / await rather than promise continuation chains, because linear control flow is easier to read and to trace:

// Discouraged
const load = () => fetchUser().then( ( user ) => render( user ) ).catch( handle )

// Preferred
const load = async () => {
    const user = await fetchUser()
    return render( user )
}

Related

• 00. Overview & Conformance
• 05. Code Formatting
• 06. Class Architecture & Returns