Uses the typescript v3.7 feature `asserts value is T` to create `assert` variants of the `is` type guards. The assertions are used to narrow types at compile time, and to throw `TypeError` at runtime for values which are not of the correct type.
```typescript
import {assert} from '@sindresorhus/is';
assert.string(foo);
```
- Each method in `is` is wrapped and mirrored in `assert`.
- Tests for `is` are duplicated for `assert`.
Notes
- The explicit typing in `interface Assert` is required for typescript to acknowledge the assertions.
- Due to the assertions requiring explicit typing, using ` property for is.assert.string()` (and so on) would require using `namespace is`, which was removed in #78. This also means that `assert` needs to be exported separately.
- Custom descriptions are used to enhance some assertion error messages. The value is not included in the error message.
- Could perhaps use Node.js' fitting `AssertionError` on the server-side, but it would require an `import`.
Fixes#91.
See
- https://github.com/sindresorhus/is/issues/91
- https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#assertion-functions
- https://github.com/microsoft/TypeScript/pull/32695
