Error Functions
An error function is a function that is created to do something with errors. They allow the user to do something about errors.
Throw If
A function that will throw an error when something is true.
ts
function throwIf(
condition: boolean,
message = "Something went wrong",
): asserts condition is falsefunction throwIf(
condition: boolean,
message = "Something went wrong",
): asserts condition is falseUsage
ts
const user = fetch('https://jsonplaceholder.typicode.com/users/1')
.then((response) => response.json())
.then((json) => json);
throwIf(!user, "There is not user here") const user = fetch('https://jsonplaceholder.typicode.com/users/1')
.then((response) => response.json())
.then((json) => json);
throwIf(!user, "There is not user here")Throw Unless
ts
function throwUnless(
condition: boolean,
message = "Something went wrong",
): asserts conditionfunction throwUnless(
condition: boolean,
message = "Something went wrong",
): asserts conditionUsage
ts
const user = fetch('https://jsonplaceholder.typicode.com/users/10')
.then((response) => response.json())
.then((json) => json);
throwUnless(user, "There is not user here")
const user = fetch('https://jsonplaceholder.typicode.com/users/10')
.then((response) => response.json())
.then((json) => json);
throwUnless(user, "There is not user here")Return Error and Result From Promise
A function that returns a potential result and a potential error. This is useful for checking if a result is returned or it's an error.
ts
function returnErrorAndResultFromPromise<T extends Promise<any>>(cb: T):
Promise<readonly [Awaited<T>, null] | readonly [null, Error]>function returnErrorAndResultFromPromise<T extends Promise<any>>(cb: T):
Promise<readonly [Awaited<T>, null] | readonly [null, Error]>Usage
ts
const [result, error] = returnErrorAndResultFromPromise(
fetch('https://jsonplaceholder.typicode.com/users/10')
.then((response) => response.json())
)
if(error) {
throw error
}
console.log(result)const [result, error] = returnErrorAndResultFromPromise(
fetch('https://jsonplaceholder.typicode.com/users/10')
.then((response) => response.json())
)
if(error) {
throw error
}
console.log(result)