You already know that promises enable us to carry out asynchronous transactions. How do you implement in your own programs? I assume you already know what promises do in Javascript](/promises-javascript) and how event driven programming works :) Javascript promise is an object. So, Promise should be as easy as using an object.

Promises enable us to carry out asynchronous transactions. Javascript promise is an object, as we all are. It is a way for the program to initiate “something”, and not wait for the process to complete (='async operations’). Runtime engine calls the call back function once the process completes - thereby completing the loop.

Javascript is an event-driven programming language. Logic is triggered by a user or system action, and the flow of action continues to be determined by events along the way. These events can be user-input like clicks, system operations like completion of DB read, completion of file load, etc. Events are handed by the event handlers that are defined by you or the underlying ecosystem.

Removing array elements while iterating through the elements in a loop can be tricky for a beginner. Consider this - 1 2 3 4 5 6 const nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; for (let i = 0; i < nums.length; i++) { console.

Here’s a quick reference of various values and their types. For further reference: see what types mean in Javascript and type casting in Javascript. Value Type Description true boolean Boolean 1 number Number “1” string String “abcd” string String Boolean(false) object Boolean object Number(0) object Number object String(“abcd”) object String object [1, 2, 3] object Array object Object() object Plain object {} object Plain object function() {} function Function object Code to cross-check -

Array constructor syntax is confusing to both the system and humans. Avoid it when possible. Consider this.. 1 2 3 const planets = ["mercury", "venus", "earth"]; console.log(planets[0]); // mercury Now, let’s say we do the same using a constructor. 1 2 3 4 const num = new Array(3, 1, 4, 5); console.

We have come to appreciate the performance and readability of the ol’ for loop. But, just how much should we be appreciating the performance? We already did a huge scientific study on different avatars of for. This is the time that we do another highly ineffective test for different types of loops so that we can prove nothing to no one.

Do not change those non-primitive function arguments without understanding the significant implications of your action. Programming languages have pass by reference and pass by value to pass arguments to a function. Javascript passes values for primitives, but references when you are trying to pass objects. Changing arguments within a function will change the arguments for ever.

Things are always not how they appear. Especially when it comes to multiplication of decimal numbers in Javascript. Consider - 1 const a = 1.1; Multiply the above number by 3. Compare with expected answer just to make sure you are not seeing a wrong answer. 1 2 3 4 5 6 const a = 1.

What if you want to allow changing props of an object, but do not want anyone to add new props? Well, that is what Object.seal is for. Objects in Javascript cannot be made immutable by using a const keyword. const works on primitives. It can also make sure you don’t reassign value to an object.

What if you want to play around with data, but also maintain metadata at the same time? In Javascript you don’t have to create other objects or work hard for that Nirvana that someone in the office was talking about. You just have to go ahead and store the darn metadata along with the object, and everyone is happy.

It is easy to take NaN for granted. But remember - the ‘not a number’ notation is the only powerful object that does not equal itself. First the essentials - you use NaN whenever you do not have variable values in control but want to do a numerical operation on it.

You can make mere variables and even an object immutable. But, how about a humble object prop? Making object props constant and immutable has practical usage. For e.g. consider this totally practical program to print out fruits and whether they are poisonous. 1 2 3 4 5 6 7 8 const eatable = { poisonous: false, printFruit: function(fruit) { return "name: " + fruit + " | poison: " + this.