A Nullable type for TypeScript.
type Nullable<T> = T | null;
This is useful for when you have strict null checking enabled, and the return of a value can possibly be null or undefined.
In the following example we attempt to get an account, which will return null | undefined if an account does not exist. We check for the null condition, and then use the get() method to retrieve the value. This allows us to avoid the use of the unsafe non-null assertion operator. The function get() will throw an error if a null value sneaks into it. This use case helps to protect refactors where the non-null assertion operator could be missed or forgotten.
const accountNullable = getAccount();
if (isNull(accountNullable)) {
createAccount();
}
const account = get(accountNullable);Alertnatively, if you can explicitly throw an error when encountering a null value.
const accountNullable = getAccount();
const account = orElseThrow(accountNullable, new Error("Account not found!"));Or, return a default value. In this example we return a new Account object when an account cannot be found.
const accountNullable = getAccount();
const account = orElse(accountNullable, new Account());Includes the following helper functions:
get<T>(x: Nullable<T>): T;
Returns the value of x, if x is defined. Throws an Error if X is null or undefined
`orElseThrow(x: Nullable, err: Error): T;
Returns the assigned value of x if x is NOT null or undefined, otherwise throws the provided Error err.
`orElse(x: Nullable, defaultVal: T): T;
Returns the assigned value of x if x is not null or undefined, otherwise returns the assigned value of defaultVal.
isNull(x: any): boolean;
Returns true if x is null, otherwise false.
isNotNull(x: any): boolean;
Returns false is x is null, otherwise true.
isUndefined(x: any): boolean;
Returns true if x is undefined, otherwise false.
isDefined(x: any): boolean;
Returns false if x is undefined, otherwise true.
isNullOrUndefined(x: any): boolean;
Returns true if x is null or undefined, otherwise false.
isNotNullorUnDefined(x: any): boolean;
Returns false if x is null or undefined, otherwise true,