Function createAssert

Creates an assert function that throws a custom error if the given condition is false.

Remarks

The returned assert function must be explicitly typed to work correctly, otherwise you will see this error:

Assertions require every name in the call target to be declared with an explicit type annotation. ts(2775)

See examples below or check out Assert on how to implement this.

Example

Basic usage

import { type Assert, createAssert, isDefined } from 'uft'

class MyError extends Error {
  constructor(code: number, message: string) {
   // ...
  }
}
// Incorrect, assert is not explicitly typed.
const assert = createAssert(MyError)
// Correct, assert is now explicitly typed.
const assert: Assert<typeof MyError> = createAssert(MyError)

assert(true, 0, 'oops') // ok
assert(false, 0, 'oops') // throws new MyError(0, 'oops')

// Error arguments can be returned from a function
// which is only called when the condition is false.
assert(false, () => [0, 'oops'])
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Type narrowing

const token: string | undefined
// might throw new MyError(401, 'missing token')
assert(token !== undefined, 401, 'missing token')
token // type: string
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