How to limit function calls in JS?-CodePudding

I need a function limitCalls (fn, maxCalls) that takes a function fn and returns a new function that can be called no more than the number of times specified in maxCalls. Test example:

 it('limitCalls', () => {
const makeIncrement = () => {
  let count = 0;

  return () => {
    count  = 1;
    return count;
  };
};

const limitedIncrementA = limitCalls(makeIncrement(), 3);

expect(limitedIncrementA()).toBe(1);
expect(limitedIncrementA()).toBe(2);
expect(limitedIncrementA()).toBe(3);
expect(limitedIncrementA()).toBe(undefined);
expect(limitedIncrementA()).toBe(undefined);

const limitedIncrementB = limitCalls(makeIncrement(), 1);

expect(limitedIncrementB()).toBe(1);
expect(limitedIncrementB()).toBe(undefined);
expect(limitedIncrementB()).toBe(undefined);

});

I have:

var calls = 0;
export default function limitCalls(fn, maxCalls) {
  if (calls >= maxCalls) {
    return undefined;
  }
  calls  = 1;
  return fn();
}

And error is limitedIncrementA is not a function. Help me please to realise it.

CodePudding user response：

In this snippet, limitedIncrementA isn't indeed a function. See this:

/* You're calling makeIncrement,
   so you're passing its return to 'limitCalls'
 */
const limitedIncrementA = limitCalls(makeIncrement(), 3);

/* Here, considering that makeIncrement exists,
   you're passing a reference to this functions,
   which can be called inside 'limitCalls'
 */
const limitedIncrementB = limitCalls(makeIncrement, 3);

So, supposing that makeIncrement returns 1, 2, 3, ..., your current code is equivalent to:

limitCalls(1, 3);

CodePudding user response：

var limitCalls = (fn, max) => {
let calls = 0
return (...args) => {
        if(calls >= max) {
            return undefined
        }
        calls  
        return  fn(...args);
    }
}

CodePudding user response：

Instead of conditionally returning a function, always return a function that conditionally executes the fn callback:

function limitCalls(fn, maxCalls) {
  let count = 0;
  
  return function(...args) {
    return count   < maxCalls && fn(...args);
  }
}

const limited = limitCalls(console.log, 3);

limited('one');
limited('two');
limited('three');
limited('four');

This code returns false if the maximum number of calls has been reached, the result of fn otherwise.