# @octetstream/invariant

Declarative errors throwing for Node.js

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## API

### `invariant(predicate, error) -> {void}`
  - **boolean** predicate – a result of some condition. Error will threw if predicate is `true`.
  - **object** error – some error object

### `invatiant(predicate, message[, ...format]) -> {void}`

  - **boolean** predicate – a result of some condition. Error will threw if predicate is `true`.
  - **string** message – an error message
  - **any** format – see more about the format in a [sprintf-js documentation](https://github.com/alexei/sprintf.js)

### `invariant(predicate, Error, message[, ...format]) -> {void}`
  - **boolean** predicate – a result of some condition. Error will threw if predicate is `true`.
  - **Function** Error – custom error class that will be used as an error constructor
  - **string** message – an error message
  - **any** format – see more about the format in a [sprintf-js documentation](https://github.com/alexei/sprintf.js)

### `invariant.reject(predicate, message[, ...format]) -> {Promise<void>}`

  Do the same things as `invariant`, but returns Promise that will be rejected when predicate is true.
  This function have same API as `invariant`.

## Example

```js
  import invariant from "@octetstream/invariant"

  // some of your code...

  // Will threw a TypeError if "value" is not a string
  invariant(typeof value !== "string", TypeError, "The value should be a string, but given type is: %s", typeof value)

  invariant(typeof value !== "string", "The value should be a string, but given type is: %s", typeof value)

  invariant(typeof value !== "string", new TypeError(`The value should be a string, but given type is: ${typeof value}`))

  // Will return rejected Promise instead of throw error synchronously
  invariant.reject(typeof value !== "string", TypeError, "The value should be a string, but given type is: %s", typeof value)
    .catch(err => console.error(err))
```