Implementation of throttle functionality in JavaScript

throttle.js

function throttle(f, t) {
  return function (args) {
    let previousCall = this.lastCall;
    this.lastCall = Date.now();
    if (previousCall === undefined // function is being called for the first time
        || (this.lastCall - previousCall) > t) { // throttle time has elapsed
      f(args);
    }
  }
}

let logger = (args) => console.log(`My args are ${args}`);
// throttle: call the logger at most once every two seconds
let throttledLogger = throttle(logger, 2000); 

throttledLogger([1, 2, 3]);
throttledLogger([1, 2, 3]);
throttledLogger([1, 2, 3]);
throttledLogger([1, 2, 3]);
throttledLogger([1, 2, 3]);

// "My args are 1, 2, 3" - logged only once

So now we have globalObject.lastCall (aka winodw.lastCall in browsers) as a result of using the throttledLogger in sloppy mode and Error in strict mode (since undefined can't hold properties) it's not nice. The solution is either 1. declare lastCall as a variable and put it in the body of throttle function directly (as an immediate child) so your anonymous function expression (the one you returns from throttle) is able to access it via closure OR 2. turn the function into named function expression and substitute this in its body to the name of the function.