Chapter 2, Thinking Functionally – A First Example
2.1 No extra variables: We can make do by using the fn variable itself as a flag. After calling fn(), we set the variable to null. Before calling fn(), we check that it’s not null by using the short-circuit && operator:
// question_02_no_extra_variables.ts
const once = <FNType extends (...args: any[]) => any>(
fn: FNType | null
) =>
((...args: Parameters<FNType>) => {
fn && fn(...args);
fn = null;
}) as FNType;
We need a small change to let TypeScript know that fn could be null; otherwise, it would object to the fn = null assignment.
2.2 Alternating functions: Like what we did in the previous question, we swap functions, and then we do the call. Here, we use a destructuring assignment to write the swap more compactly. For more information, refer to developer.mozilla.org/en-US/docs/Web/JavaScript...
