Implement a sampling function

Mar 27, 2024

Sampling is a higher order utility function which invokes a function every n sample period. For other invocation which are not within the sampling period, it can return undefined.

Variation: Basic implementation

1. Basic Implementation

function sampling(fn, n) {
  let invocations = 0;

  function samplingFnImpl(...args) {
    invocation++;
    if (invocations % n !== 0) {
      return undefined;
    }

    return fn.call(this, ...args);
  }

  return samplingFnImpl;
}

// Usage of the sampling utility function
const sampledFn = sampling(() => {
  console.log('I will be called on every 3rd sampling period');
}, 3);

sampledFn();
sampledFn();
sampledFn(); // yields logs here on 3th sample period
sampledFn();
sampledFn();
sampledFn(); // yields logs here on 6th sample period
// ... so on

Variation: With Last Result

2. Variation with last result

In this variation, if the function is invoked in non-sampling period, we simply need to return the last result saved during the sampling period invocation of function.

function sampling(fn, n) {
  let invocations = 0;
  let lastResult = undefined;

  function samplingFnImpl(...args) {
    invocation++;
    if (invocations % n !== 0) {
      // simply return last saved result instead of undefined
      return lastResult;
    }

    // save result of function invocation
    lastResult = fn.call(this, ...args);
    return lastResult;
  }

  return samplingFnImpl;
}

// Usage of the sampling utility function
const sampledFn = sampling(() => {
  console.log('I will be called on every 3rd sampling period');
}, 2);

sampledFn();
sampledFn(); // yields logs here on 2nd sample period
sampledFn();
sampledFn(); // yields logs here on 4th sample period
sampledFn();
sampledFn(); // yields logs here on 6th sample period
// ... so on

Implement a sampling function

1. Basic Implementation

2. Variation with last result

Further Reading