# p-wait-for > Wait for a condition to be true Can be useful for polling. ## Install ``` $ npm install p-wait-for ``` ## Usage ```js const pWaitFor = require('p-wait-for'); const pathExists = require('path-exists'); (async () => { await pWaitFor(() => pathExists('unicorn.png')); console.log('Yay! The file now exists.'); })(); ``` ## API ### pWaitFor(condition, options?) Returns a `Promise` that resolves when `condition` returns `true`. Rejects if `condition` throws or returns a `Promise` that rejects. #### condition Type: `Function` Expected to return `Promise<boolean> | boolean`. #### options Type: `object` ##### interval Type: `number`\ Default: `20` Number of milliseconds to wait before retrying `condition`. ##### timeout Type: `number`\ Default: `Infinity` Number of milliseconds to wait before automatically rejecting. ##### leadingCheck Type: `boolean`\ Default: `true` Whether to run the check immediately rather than starting by waiting `interval` milliseconds. Useful for when the check, if run immediately, would likely return `false`. In this scenario, set `leadingCheck` to `false`. ## Related - [p-whilst](https://github.com/sindresorhus/p-whilst) - Calls a function repeatedly while a condition returns true and then resolves the promise - [More…](https://github.com/sindresorhus/promise-fun)
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