📄 Table of Contents

• Closures
• why to use Closures
• Disadvantages of using Closures in javascript
• Alternatives of Closures

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◉ Closures

A Closure is a named or anonymous function defined within the context of an object or any other function, which preserves and access to the context where it was declared.

In JS, variables defined outside a function are automatically available inside the function (but NOT vice versa) because JS uses “Lexical Scoping” & it achieves so using Closures (or inner functions).

• In JavaScript, all functions work like closures which literally means closures are created every time a function is created, at…

📄 Table of Contents

• how to write a callback function
• Polyfills for .forEach(), .map() and .filter()

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Introduction

In simple word, A polyfill is a piece of javascript code which provide native support to the older browsers who does NOT have the support of modern functionalities of javascript.

In ECMAScript 2015, there are many new Array methods has been added to manipulate an arrays in a simple and easy way. Here we are trying to create polyfills for .forEach(), .map() and .filter() methods.

Prior to writting polyfills, let’ s understand how to write callback functions?

How to write callback functions

A callback function is a function…

Objects are reference types, so you can’t use your normal equality operators, i.e. == or ===. as you use for comparison of primitives.

As the name suggests JSON.stringify() converts objects to strings first and comparison takes place afterward.

JSON.stringify({ a: 1, b: 2}) === "{"a":1,"b":2}"

JSON.stringify({ b: 2, a: 1}) === "{"b":2,"a":1}"

For JSON. stringify() , the order matters.

So if the key-value pair are ordered differently in the two objects but are the same, it will return false. Whereas it doesn’t matter in Lodash isEqual , it will return true as along as the key-value pair exists.

Also, it…

While it is technically possible to alter state by writing to this.state directly, it will not lead to the Component re-rendering with new data, and generally lead to state inconsistency.

Three Rules of Thumb When Using setState( )

Do Not Modify State Directly

State Updates May Be Asynchronous

React may batch multiple setState() calls into a single update for performance.

Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state.

A preflight request is a small request that is sent by the browser before the actual request. It contains information like which HTTP method is used, as well as if any custom HTTP headers are present. The preflight gives the server a chance to examine what the actual request will look like before it’s made.

1. Introduction

Sometimes HTTP requests, triggered from JavaScript on our webpage, are preceded by an OPTIONS request.

In this tutorial, we’ll look at why this additional request is sent.

Next, we’ll take a look at how to suppress this so-called preflight request. …

Here is how’s your DOM structured in the browser.

…newest version of react in oct’2020

React 17 is was advertised as a No New Feature release. However, you can find several high-impact improvements to React core. Out of these, the changes for JSX is quite noticeable.

Ideally when you upgrade from React 16 to 17, you must upgrade the whole project at once.

However, from React 17 onwards, there will be two upgrade options. Hereafter, you can decide to upgrade the entire project at once or in parts to the latest version.

Besides, there are many other changes in React 17 like New JSX Transform, Effect Cleanup Timing, Native…

Avoiding runtime errors using frontend monitoring tools

As developers, we always push our limits to test our applications before they go live. As we all know, no matter how far we test, runtime issues are inevitable. Therefore, monitoring every aspect of the application is a must.