JavaScript Tips

JavaScript Tips — Randomness and Arrays

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Like any kind of apps, JavaScript apps also have to be written well.

Otherwise, we run into all kinds of issues later on.

In this article, we’ll look at some tips we should follow when writing JavaScript code.

Get a Random Number in a Specific Range

We can get a random number from a specify range with the Math.random() method.

For example, we can write:

const min = 2;
condt max = 10;
const x = Math.floor(Math.random() * (max - min + 1)) + min;

Since Math.random() only returns a number between 0 and 1, we’ve to multiply what it returns with max — min + 1 .

Then we add that to min to make it within range.

Generate an Array of Numbers with Numbers from 0 to Max

We can create an array of numbers by using a for loop.

For example, we can write:

let numbersArray = [] , max = 100;

for (let i = 1; numbersArray.push(i++) < max);

We use the for loop to increment i by 1 with each iteration.

And then we end with we reach max — 1 .

i++ increments and returns the number we return.

Generate a Random Set of Alphanumeric Characters

We can create a random set of alphanumeric characters by using the toString and substr methods.

For instance, we can write:

function generateRandomAlphaNum(len) {
  let randomString = "";
  while (randomString.length < len) {
    randomString += Math.random()
  return randomString.substr(0, len);

We have the generateRandomAlphaNum function.

And we use the while loop to generate the string up to the given len value.

To generate the character we use the Math.random() with the toString and substr calls to create the character.

Shuffle an Array of Numbers

We can shuffle an array of number with the sort method.

For example, we can write:

const numbers = [5, 2, 4, 3, 6, 2];
numbers = numbers.sort(() => { return Math.random() - 0.5});

We return a random number that’s positive or negative so that the order is switched only when it’s positive.

That’s random so we shuffle them.

A String Trim Function

We can trim all whitespace with the replace method and some regex.

For example, we can write:

str.replace(/^s+|s+$/g, "")

We trim all whitespace with the regex.

JavaScript strings also have the trim method to do the trimming.

Append an Array to Another Array

To append an array to another array, we can use the spread operator with push .

For example, we can write:


We can also use the spread operator without push :

const arr = [...arr1, ...arr2];

Transform Arguments into an Array

We can get arguments as an array with the rest operator.

For example, if we have:

const foo = (...args) => {}

Then whatever we have in args will be an array.

We can pass in anything into foo and it’ll end up in args .


We can generate random entities with the Math.random method.

Also, we can append items to arrays and get arguments.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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