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# `tiny-invariant` 🔬💥
[](https://travis-ci.org/alexreardon/tiny-invariant)
[](https://www.npmjs.com/package/tiny-invariant) [](https://david-dm.org/alexreardon/tiny-invariant)
[](https://www.npmjs.com/package/tiny-invariant)
[](https://www.npmjs.com/package/tiny-invariant)
A tiny [`invariant`](https://www.npmjs.com/package/invariant) alternative.
## What is `invariant`?
An `invariant` function tasks a value, and if the value is [falsy](https://github.com/getify/You-Dont-Know-JS/blob/bdbe570600d4e1107d0b131787903ca1c9ec8140/up%20%26%20going/ch2.md#truthy--falsy) then the `invariant` function will throw. If the value is [truthy](https://github.com/getify/You-Dont-Know-JS/blob/bdbe570600d4e1107d0b131787903ca1c9ec8140/up%20%26%20going/ch2.md#truthy--falsy), then the function will not throw.
```js
import invariant from 'tiny-invariant';
invariant(truthyValue, 'This should not throw!');
invariant(falsyValue, 'This will throw!');
// Error('Invariant violation: This will throw!');
```
## Why `tiny-invariant`?
The [`library: invariant`](https://www.npmjs.com/package/invariant) supports passing in arguments to the `invariant` function in a sprintf style `(condition, format, a, b, c, d, e, f)`. It has internal logic to execute the sprintf substitutions. The sprintf logic is not removed in production builds. `tiny-invariant` has dropped all of the sprintf logic. `tiny-invariant` allows you to pass a single string message. With [template literals](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) there is really no need for a custom message formatter to be built into the library. If you need a multi part message you can just do this: `invariant(condition, 'Hello, ${name} - how are you today?')`
## API: `(condition: mixed, message?: string) => void`
- `condition` is required and can be anything
- `message` is an optional string
## Installation
```bash
# yarn
yarn add tiny-invariant
# bash
npm add tiny-invariant --save
```
## Dropping your `message` for kb savings!
We recommend using [`babel-plugin-dev-expression`](https://www.npmjs.com/package/babel-plugin-dev-expression) to remove the `message` argument from your `invariant` calls in production builds to save kbs!
What it does it turn your code that looks like this:
```js
invariant(condition, 'My cool message that takes up a lot of kbs');
```
Into this
```js
if (!condition) {
if ('production' !== process.env.NODE_ENV) {
invariant(false, 'My cool message that takes up a lot of kbs');
} else {
invariant(false);
}
}
```
Your bundler can then drop the code in the `"production" !== process.env.NODE_ENV` block for your production builds
Final result:
```js
if (!condition) {
invariant(false);
}
```
> For `rollup` use [rollup-plugin-replace](https://github.com/rollup/rollup-plugin-replace) and set `NODE_ENV` to `production` and then `rollup` will treeshake out the unused code
>
> [`Webpack` instructions](https://webpack.js.org/guides/production/#specify-the-mode)
## Builds
- We have a `es` (EcmaScript module) build (because you _know_ you want to deduplicate this super heavy library)
- We have a `cjs` (CommonJS) build
- We have a `umd` (Universal module definition) build in case you needed it
We expect `process.env.NODE_ENV` to be available at module compilation. We cache this value
## That's it!
🤘
|
