Compose functions and arguments safely
Compose functions while preserving argument tuples and return types; write pipe/compose helpers that stay type-safe.
Compose functions and arguments safely is a free TypeScript Academy lesson on CoddyKit. This is lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The TypeScript Academy course includes 3 lessons in total.
Intro
Goal: Compose functions without losing argument info. Variadic tuples let you keep the full args tuple through pipe/compose helpers.
- Preserve arity and names
- Keep inference across steps
- No
any, no casts
Basic compose
compose: The first function takes all arguments (...args: A), the second consumes its output; arity and types are preserved.
function compose<A extends any[], B, C>(g: (b: B) => C, f: (...args: A) => B) {
return (...args: A): C => g(f(...args))
}
function toLen(a: string, n: number) { return `${a}${n}`.length }
function isEven(x: number) { return x % 2 === 0 }
const c1 = compose(isEven, toLen)
const ok = c1("id", 99) // booleanPipe helper
pipe implements the same idea in reverse order; inference flow is more intuitive.
function pipe<A extends any[], B, C>(f: (...args: A) => B, g: (b: B) => C) {
return (...args: A): C => g(f(...args))
}
const p1 = pipe(toLen, isEven)
const ok2 = p1("xx", 7) // booleanCompose 3+
3+ functions: the same pattern is repeated; tuple A is preserved, and intermediate returns are chained.
function compose3<A extends any[], B, C, D>(h: (c: C) => D, g: (b: B) => C, f: (...args: A) => B) {
return (...args: A): D => h(g(f(...args)))
}
function toUpper(s: string) { return s.toUpperCase() }
const c3 = compose3(toUpper, (x: number) => x.toString(), toLen)
const val = c3("a", 5) // "2" → then upper → "2"Bind head
bindHead: Prefix full arguments and generate a 0-arg function; for demo purposes only (actually, it can be made more flexible with Parameters).
function bindHead<A extends any[], B>(fn: (...args: A) => B, ...head: A) {
return (...rest: []): B => fn(...head)
}
const bh = bindHead(toLen, "x", 42)
const r = bh() // numberTips
Tips:
Avoid any in helpers; it breaks the inference chain.
If necessary, make the return type explicit; this increases dev experience.
For multi-stage composition, choose small helpers instead of overly generic ones.
Compose signature check
Quick check: Which compose signature preserves the source argument tuple?
Recap
Recap: You wrote compose/pipe while preserving arguments with variadic tuples; the stream is established without losing arity and types.
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Frequently Asked Questions
Is the “Compose functions and arguments safely” lesson free?
Yes — the full text of “Compose functions and arguments safely” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO. The TypeScript Academy course includes 3 lessons in total.
What will I learn in “Compose functions and arguments safely”?
Compose functions while preserving argument tuples and return types; write pipe/compose helpers that stay type-safe. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start TypeScript Academy?
No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 3.
How long does the “Compose functions and arguments safely” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this TypeScript Academy lesson?
Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Tuple rest elements, curry types
- Compose functions and arguments safely
- Strongly-typed builders