google-style-ts

Google JavaScript / TypeScript style — applied rules

You are editing JS/TS code. Every line you write must satisfy the Google JavaScript Style Guide and the Google TypeScript Style Guide. The full extract is in docs/standards/google-js-ts-style.md. The machine-checkable subset is in rubric/RUBRIC.yaml (rules g-ts-*).

Required patterns (must do)

• const by default, let only when reassignment is needed; never var. (RUBRIC g-ts-003, jsguide#features-use-const-and-let)
• One variable per declaration: let a = 1; let b = 2; not let a = 1, b = 2;.
• === and !== always; the only exception is == null to catch both null and undefined. (g-ts-005, tsguide#equality-checks)
• Throw new Error(...) (or a subclass) only — never strings, never plain objects. Always include new. (g-ts-009)
• catch (e: unknown), narrow via instanceof Error. Empty catch blocks must carry a comment explaining why.
• Function declarations for named functions (function foo() {}); arrow functions for callbacks and expressions.
• for…of for arrays; for…in only on dict objects with a hasOwnProperty guard.
• Mark unchanged class fields readonly; prefer parameter properties: constructor(private readonly svc: Svc) {}.
• Initialize fields at declaration when possible.

Forbidden patterns (must not do)

• var, with, eval, new Function(string), debugger; in production code. (g-ts-003, g-ts-004, g-ts-010)
• const enum, #privateField, public modifier (except on parameter properties), obj['foo'] to bypass visibility.
• Prototype manipulation, mixins, monkey-patching builtins.
• new String/Boolean/Number/Symbol wrapper instantiations.
• Array(x1, x2, x3) constructor — use [x1, x2, x3].
• +x unary plus or parseInt(x) for base-10 — use Number(x) + isFinite.
• Default exports — always use named exports. (g-ts-002)
• any without an explicit suppression comment justifying it. Prefer unknown and narrow. (g-ts-006)
• Wrapper types String, Boolean, Number, Object — use lowercase primitives.
• |undefined in type aliases — use ? optional fields.
• <Foo>x type assertion syntax — use x as Foo. Double-assert via unknown.
• Non-null assertion ! without a justifying comment.

Naming (g-ts-001)

Kind	Style	Example
Class / interface / type / enum / decorator / type-param	UpperCamelCase	class Request, interface Readable
Variable / parameter / function / method / property / module alias	lowerCamelCase	sendMessage, customerId
Module-level immutable constants and enum members	CONSTANT_CASE	const MAX_RETRIES = 3
TS file names	snake_case	import * as fooBar from './foo_bar'
Acronyms in identifiers	Treat as words	loadHttpUrl, not loadHTTPURL

No _ prefix or suffix; no IFoo Hungarian; no $ prefix (except framework requirements); one-letter names only in scopes ≤10 lines.

Imports

• Use modules, not namespaces. No ///<reference>, no namespace Foo {}.
• Named exports only (export class Foo {}); no export default.
• Type-only imports: import type {Foo} from './foo'; or inline import {type Foo, Bar} from './foo';.
• Relative paths for same-project files; minimize ../../...

Comments / JSDoc

• /** … */ for documentation; // for implementation comments.
• Document every top-level export of a module. (g-ts-011)
• No type annotations in TS JSDoc (@param {string}, @implements, @private, @override, @enum — TypeScript syntax already conveys it).
• Method descriptions start with a third-person verb: "Computes…", "Returns…".

Formatting (g-ts-012, delegated to Prettier with the Google preset)

2-space indent, 80-col wrap, single quotes, semicolons required, K&R braces, trailing commas where the closing bracket is on its own line.

When you write or edit code

1. Cite rule IDs in the commit message body when you make a non-trivial style choice (e.g. "named export per g-ts-002").
2. If you must violate a rule (e.g. test fixture needs any), include a comment on the offending line: // SUPPRESS g-ts-006: <reason>.
3. Run bash rubric/runner.sh --diff --md before declaring done; resolve P0 findings, address P1 findings or justify them.
4. Refuse changes that bundle reformatting + logic — split into a pure-format CL first per Google eng-practices.