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Contents
const isProduction: boolean = process.env.NODE_ENV === 'production';
const prefix: string = 'Invariant failed';
/**
* `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).
*
* 💥 `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)
*
* 🤏 `message`s are not displayed in production environments to help keep bundles small
*
* @example
*
* ```ts
* const value: Person | null = { name: 'Alex' };
* invariant(value, 'Expected value to be a person');
* // type of `value`` has been narrowed to `Person`
* ```
*/
export default function invariant(
condition: any,
// Not providing an inline default argument for message as the result is smaller
/**
* Can provide a string, or a function that returns a string for cases where
* the message takes a fair amount of effort to compute
*/
message?: string | (() => string),
): asserts condition {
if (condition) {
return;
}
// Condition not passed
// In production we strip the message but still throw
if (isProduction) {
throw new Error(prefix);
}
// When not in production we allow the message to pass through
// *This block will be removed in production builds*
const provided: string | undefined = typeof message === 'function' ? message() : message;
// Options:
// 1. message provided: `${prefix}: ${provided}`
// 2. message not provided: prefix
const value: string = provided ? `${prefix}: ${provided}` : prefix;
throw new Error(value);
}
Version data entries
15 entries across 15 versions & 1 rubygems