| 1 | /**
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| 2 | * `invariant` is used to [assert](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions) that the `condition` is [truthy](https://github.com/getify/You-Dont-Know-JS/blob/bdbe570600d4e1107d0b131787903ca1c9ec8140/up%20%26%20going/ch2.md#truthy--falsy).
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| 3 | *
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| 4 | * 💥 `invariant` will `throw` an `Error` if the `condition` is [falsey](https://github.com/getify/You-Dont-Know-JS/blob/bdbe570600d4e1107d0b131787903ca1c9ec8140/up%20%26%20going/ch2.md#truthy--falsy)
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| 5 | *
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| 6 | * 🤏 `message`s are not displayed in production environments to help keep bundles small
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| 7 | *
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| 8 | * @example
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| 9 | *
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| 10 | * ```ts
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| 11 | * const value: Person | null = { name: 'Alex' };
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| 12 | * invariant(value, 'Expected value to be a person');
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| 13 | * // type of `value`` has been narrowed to `Person`
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| 14 | * ```
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| 15 | */
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| 16 | export default function invariant(condition: any,
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| 17 | /**
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| 18 | * Can provide a string, or a function that returns a string for cases where
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| 19 | * the message takes a fair amount of effort to compute
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| 20 | */
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| 21 | message?: string | (() => string)): asserts condition;
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