function debounce(fn, delay) {
    let timer;

    function helper(...args) {
        clearTimeout(timer);
        timer = setTimeout(() => {
            fn.apply(this, args); // keep the original context
        }, delay);
    }

    return helper;
}

// ------------Test----------
// var test = {
//   value: 'test',
//   changeInput: function(key) {
//     console.log('Input changed', key, this.value);
//   }
// }
// test.changeInput = debounce(test.changeInput, 1000);

// for(let i = 0; i <= 10; i++) {
//   test.changeInput(i);
// }

// Output 'Input changed', 10, 'test'
// Only triggered once.