23 lines
1.1 KiB
TypeScript
23 lines
1.1 KiB
TypeScript
/**
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* `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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* 💥 `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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* 🤏 `message`s are not displayed in production environments to help keep bundles small
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*
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* ```ts
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* const value: Person | null = { name: "Alex" };
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* invariant(value, "Expected value to be a person");
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* // type of `value`` has been narrowed to `Person`
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* ```
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*/
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export default function invariant(
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condition: any,
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message?: string | (() => string),
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): asserts condition {
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if (condition) return;
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const resolvedMessage: string | undefined = typeof message === "function" ? message() : message;
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const prefix = "[Invariant Violation]";
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const value = resolvedMessage ? `${prefix}: ${resolvedMessage}` : prefix;
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throw new Error(value);
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}
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