40 lines
893 B
Markdown
40 lines
893 B
Markdown
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# Assert Never [![npm version][npm-image]][npm-url]
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Helper function for [exhaustive checks][exhaustive-checks] of discriminated
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unions in TypeScript.
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## Installation
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```
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npm install --save assert-never
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```
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## Usage
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```ts
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import {assertNever} from "assert-never";
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type A = {type: 'a'};
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type B = {type: 'b'};
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type Union = A | B;
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function doSomething(arg: Union) {
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if (arg.type === 'a') {
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return something;
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}
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if (arg.type === 'b') {
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return somethingElse;
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}
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// TS will error if there are other types in the union
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// Will throw an Error when called at runtime. Use `assertNever(arg, true)`
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// instead to fail silently.
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return assertNever(arg);
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}
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```
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[npm-image]: https://badge.fury.io/js/assert-never.svg
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[npm-url]: https://badge.fury.io/js/assert-never
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[exhaustive-checks]: https://basarat.gitbook.io/typescript/type-system/discriminated-unions#exhaustive-checks
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