JS Qs

debounce.js

// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
function debounce(func, wait, immediate) {
	var timeout;
	return function() {
		var context = this, args = arguments;
		var later = function() {
			timeout = null;
			if (!immediate) func.apply(context, args);
		};
		var callNow = immediate && !timeout;
		clearTimeout(timeout);
		timeout = setTimeout(later, wait);
		if (callNow) func.apply(context, args);
	};
};


var myEfficientFn = debounce(function() {
	// All the taxing stuff you do
}, 250);

window.addEventListener('resize', myEfficientFn);

flatten.js

// higher-order function that takes an array as input and returns a reducer
// a reducer function (a pure fn, same input = same output) takes the previous state
// and an action, and then returns the next state
// referred to as a reducer because you pass to Array.prototype.reduce
// const reducer = (accumulator, currentValue) => accumulator + currentValue
const flatten = (arr) => {
  const reducer = (flat, toFlatten) => {
    return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten);
  };
  return arr.reduce(reducer, []);
}

const arrStrInt = [["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]];
const arrNested = [[[1, [1.1]], 2, 3], [4, 5]];
const arrInsane = [[1,[2,[[3]]]],4,[5,[[[6]]]]];
const arrObj = [
  {
    id: 1,
    country: [
      {
        id: "5a60626f1d41c80c8d3f8a85"
      },
      {
        id: "5a6062661d41c80c8b2f0413"
      }
    ]
  },
  {
    id: 2,
    country: [
      {
        id: "5a60626f1d41c80c8d3f8a83"
      },
      {
        id: "5a60626f1d41c80c8d3f8a84"
      }
    ]
  }
];

console.log(flatten(arrStrInt))
console.log(flatten(arrNested))
console.log(flatten(arrObj))
console.log(flatten(arrInsane))

this.txt

implicit binding

explicit binding uses call, bind, or apply
  bind returns a new function instead of immediately invoking it

new Binding
  using the keyword
  
 Lexical binding
 window binding
  the global object