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# tiny-invariant 🔬💥

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A tiny [`invariant`](https://www.npmjs.com/package/invariant) alternative.
`tiny-invariant` is a _tiny_, widely-supported, zero-dependency alternative to [`invariant`](https://www.npmjs.com/package/invariant).

`tiny-invariant` - when every byte counts!

## What is `invariant`?

An `invariant` function takes 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
```ts
import invariant from 'tiny-invariant';

invariant(truthyValue, 'This should not throw!');
Expand All @@ -22,23 +23,23 @@ invariant(falsyValue, 'This will throw!');
```

## Why `tiny-invariant`?
`tiny-invariant` is a *tiny*, widely-supported, zero-dependency alternative to [`invariant`](https://www.npmjs.com/package/invariant). See below for details on just how compact it can get.

`tiny-invariant` - when every byte counts!

## Error Messages

`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:
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 code for `sprintf` logic and instead encourages consumers to leverage [template literals](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) for message formatting.

```js
```ts
invariant(condition, `Hello, ${name} - how are you today?`);
```

You can also provide a function to generate your message, for when your message is expensive to create
## Error Messages

`tiny-invariant` allows you to pass a `string` message, or a function that returns a `string` message. Using a function that returns a message is helpful when your message is expensive to create.

```js
```ts
import invariant from 'tiny-invariant';

invariant(condition, `Hello, ${name} - how are you today?`);

// Using a function is helpful when your message is expensive
invariant(value, () => getExpensiveMessage());
```

Expand Down Expand Up @@ -73,13 +74,13 @@ npm install tiny-invariant --save

Big idea: you will want your compiler to convert this code:

```js
```ts
invariant(condition, 'My cool message that takes up a lot of kbs');
```

Into this:

```js
```ts
if (!condition) {
if ('production' !== process.env.NODE_ENV) {
invariant(false, 'My cool message that takes up a lot of kbs');
Expand All @@ -94,7 +95,7 @@ if (!condition) {

Your bundler can then drop the code in the `"production" !== process.env.NODE_ENV` block for your production builds to end up with this:

```js
```ts
if (!condition) {
invariant(false);
}
Expand Down

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