category: Javascript

Let us see how we could use a reusable function that can ‘memoize’ any given function. Memoization is a technique that can be used in long, recursive code to cache results from previous executions and speed up the overall process. Previously we have seen an overview memoization in JS with an example of generating Fibonacci series using such techniques. But, what if you want to apply that for multiple operations? Say, you are building a super-calculator that outputs Fibonacci series, factorial of a number, sum-product of repeat combinations, etc. ...

Let’s say you have to write a function that doubles a given number. You also find out that you may get one number (in which case double that number), or multiple numbers (double all numbers). The first thought that comes to mind is to - use different functions (or) check type of input and process differently Consider the below code - const double = x => { if (typeof x == "object") return x.map(val => val * 2); else return x * 2; }; console.log(double(2)); // 4 console.log(double([2, 3])); // [ 4, 6 ] The given option is workable, but there is a shortcut way to do the same. ...

Write a simple logic to shuffle a given array. Consider this array - const nums = [1, 2, 3, 4, 5, 6]; You can shuffle this array by using the following code - const nums = [1, 2, 3, 4, 5, 6]; nums.sort(() => Math.random() - Math.random()); console.log(nums); /* [ 1, 4, 5, 2, 6, 3 ] [ 6, 1, 4, 2, 5, 3 ] ... */ Each run of the routine will give you a different array, thanks to Math.random() expression. Subtracting one random number from the other can give you a positive or negative result - so the sort can be totally different and random. ...

How do you round-off a number in Javascript? The simple way - console.log(Math.round("3.14")); // 3 console.log(Math.round("3.72")); // 4 Then, there are other interesting ways.. Round off to the nearest lower whole number Use Math.floor instead of round. console.log(Math.floor("3.14")); // 3 console.log(Math.floor("3.72")); // 3 Round off to the nearest higher whole number Use ceil. console.log(Math.ceil("3.14")); // 4 console.log(Math.ceil("3.72")); // 4 Just truncate the fraction Use trunc. console.log(Math.trunc("3.14")); // 3 console.log(Math.trunc("3.72")); // 3 Use a simple, fast way using ~~ The double tilde operator has an output like trunc. ...

What is memoization and where is it useful? Let us do a quick overview and dig into example code. Memoization is a technique that can be used in long, recursive code to cache results from previous executions and speed up the overall process. Consider a long repetitive operation where there is a good possibility that you will have the same arguments for the computation function more than once. What if we could make our program remember what had transpired in the last execution. We could then effectively shave-off cycles that had been done previously and speed up execution. ...

How do global variables impact async functions? Does hoisting have a role to play at all? As many beginners have found out the hard way - yes. for (var i = 0; i < 5; i++) { setTimeout(function() { console.log(i); }, 500 * i); } What’s the output you’d expect? // 0 1 2 3 4 What you get - // 5 5 5 5 5 If you have not already figured it out, the behaviour is because of the var used in for loop. ...

What is the easiest way to find maximum and minimum of a given set of numbers? Well, that’s easy. console.log(Math.max(1, 3, 5)); console.log(Math.min(1, 3, 5)); // 5 1 How about an array? The first thing that comes to mind.. const nums = [1, 3, 5]; const max = nums.reduce((n, mx) => (n > mx ? n : mx)); console.log("max: ", max); const min = nums.reduce((n, mn) => (n < mn ? n : mn)); console.log("min: ", min); // 5 1 But, an easier solution is right in front of us. console.log(Math.max(...nums)); console.log(Math.min(...nums)); // 5 1 Moral of the story Never trust the first instinct. But, you are not likely to be as naïve as me - so YMMV.

Access an array in reverse. Consider the array in the code block below - const nums = [1, 2, 3]; Accessing the array is easy enough. console.log(nums[0]); console.log(nums[1]); console.log(nums[2]); /* 1 2 3 */ But, what if you want to access the array from the last element? Use pop We have seen one of the ways to do that using pop. console.log(nums.pop()); console.log(nums.pop()); console.log(nums.pop()); /* 3 2 1 */ But, this changes the array. console.log(nums); // [] Use slice If you want to just access the array from the last element, but not change the array - ...

How about using the spread operator for handling optional arguments, or for null arguments? Consider this code - function sum(x, y, z) { return x + y + z; } We can choose to pass ‘z’ or not, but ignoring ‘y’ returns an error. console.log(sum(1, 2, 3)); // 6 console.log(sum(1, 2)); // NaN console.log(sum(1, , 3)); // error: Unexpected token , Sure, you can use a null or undefined in the middle and get away with it. But, you could also replace that with the spread operator like so - ...

Encapsulate a console.log() in a function and use it anywhere - even within the most complex expressions. The most typical console.log - console.log("hello world"); // hello world Change it to - function logThis(expr) { console.log(expr); return expr; } logThis("hello world"); // hello Why the circus? Well, consider you are debugging this really serious planet array marked for destruction. const planets = [ { name: "mercury", position: 1 }, { name: "venus", position: 2 }, { name: "earth", position: 3 } ]; console.log(planets.sort().filter(planet => planet.position == 3)); Sure, you can unchain the chain and debug. console.log(planets); console.log(planets.sort()); console.log(planets.sort().filter(planet => planet.position == 3)); But, there is no joy in the above code (and in the destruction task I might add). Is there? ...