# Delay the evaluation of a function

Turn a call into a thunk: a function that runs the call only when invoked.

Canonical: https://1loc.dev/function/delay-the-evaluation-of-a-function/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Usage lines executed in Node.js 22 and headless Chromium; no external services
Updated: 2026-10-28

## Implementation

```javascript
function thunkify(fn) { return (...args) => () => fn(...args); }
```

## Usage

```javascript
let calls = 0;
const render = name => (calls += 1, 'Hello, ' + name);
const later = thunkify(render)('Ana');
calls; // → 0
later(); // → 'Hello, Ana'
calls; // → 1
```

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

## Limits

- The thunk runs fn every time it is called; wrap it with Execute a function once to keep the first result.
- The original named it thunkfy.

The function does not validate its arguments. Add checks where it receives untrusted input.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/delay-the-evaluation-of-a-function.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Documented as a reference with executed usage lines. Original MDX retained as inert source evidence.