Null vs. Undefined: What's the Difference?

At first glance, null and undefined may seem the same, but they are far from it. This article will explore the differences and similarities between null and undefined in JavaScript.

What is null?

There are two features of null you should understand:

  • null is an empty or non-existent value.
  • null must be assigned.

Here’s an example. We assign the value of null to a:

let a = null;console.log(a);
// null

What is undefined?

Undefined most typically means a variable has been declared, but not defined. For example:

let b;console.log(b);
// undefined

You can also explicitly set a variable to equal undefined:

let c = undefined;console.log(c);
// undefined

Finally, when looking up non-existent properties in an object, you will receive undefined:

var d = {};console.log(d.fake);
// undefined

Similarities between null and undefined

In JavaScript there are only six falsy values. Both null and undefined are two of the six falsy values. Here’s a full list:

  • false
  • 0 (zero)
  • “” (empty string)
  • null
  • undefined
  • NaN (Not A Number)

Any other value in JavaScript is considered truthy.

Also in JavaScript, there are six primitive values. Both null and undefined are primitive values. Here is a full list:

All other values in JavaScript are objects (objects, functions, arrays, etc.).

Interestingly enough, when using typeof to test null, it returns object:

let a = null;
let b;console.log(typeof a);
// objectconsole.log(typeof b);
// undefined

This has occurred since the beginning of JavaScript and is generally regarded as a mistake in the original JavaScript implementation.

null !== undefined

As you can see so far, null and undefined are different, but share some similarities. Thus, it makes sense that null does not strictly equal undefined.

null !== undefined 

But, and this may surprise you, null loosely equals undefined.

null == undefined

In JavaScript, a double equals tests for loose equality and preforms type coercion. This means we compare two values after converting them to a common type.

Practical Differences

All of this is great, but what about a practical difference between null and undefined?

Consider the following code snippet:

let logHi = (str = 'hi') => {
  console.log(str);
}

The code above creates a function named logHi. This function requires one parameter and sets the default of that parameter to hi if it isn’t supplied. Here’s what that looks like:

logHi();
// hi

We can also supply a parameter to overwrite this default:

logHi('bye');
// bye

With default parameters, undefined will use the default while null does not.

logHi(undefined);
// hilogHi(null);
// null

Summary

  • null is an assigned value. It means nothing.
  • undefined typically means a variable has been declared but not defined yet.
  • null and undefined are falsy values.
  • null and undefined are both primitives. However an error shows that typeof null = object.
  • null !== undefined but null == undefined.

#javascript

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Null vs. Undefined: What's the Difference?
Autumn  Blick

Autumn Blick

1598839687

How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

  • Performance: It delivers optimal performance.
  • Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
  • UI design: React Native enables you to design simple and responsive UI for your mobile app.
  • 3rd party plugins: This framework supports 3rd party plugins.
  • Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

  • Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
  • Near-native user experience: React Native provides several native components, and these are platform agnostic.
  • The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

#android app #frontend #ios app #mobile app development #benefits of react native #is react native good for mobile app development #native vs #pros and cons of react native #react mobile development #react native development #react native experience #react native framework #react native ios vs android #react native pros and cons #react native vs android #react native vs native #react native vs native performance #react vs native #why react native #why use react native

akshay L

akshay L

1572701335

Lean vs Agile vs Waterfall | What is Lean | Difference between Waterfall and Agile

In this video you will learn the difference between waterfall and agile model, what is lean, lean vs agile vs waterfall differences in detail.

Why DevOps is important?

DevOps implementation is going through the roof with most of the largest software organizations around the world invested heavily in its implementation. The core values of devops is effectively based on the Agile Manifesto but with one slight change which moves the focus from creating a working software to one that is more interested in the end-to-end software service mechanism and delivery.

#agile vs waterfall vs lean #Learn Lean #What is Lean #Waterfall vs Agile #Difference Between Waterfall and Agile

Aisu  Joesph

Aisu Joesph

1624980180

Understanding the difference between null and undefined in Azure Cosmos DB

This blog is part two of a series of three blogs (read part one here) where we’ll demystify commonly confused concepts for developers learning how to query data using the SQL (Core) API in Azure Cosmos DB. We’ll look at the difference between null and undefined values.

The value null must be explicitly set for a property. For example, here is an item that has the creationDate property set to null:

{
  "id": "AndersenFamily",
  "lastName": "Andersen",
  "address": {
      "state": "WA",
      "county": "King",
      "city": "Seattle"
      },
  "creationDate": null
}

A property with a **null **value must have it explicitly assigned. Properties not defined in an item have an undefined value. In the example item above, the property **isRegistered **has a value of undefined because it is omitted from the item.

Azure Cosmos DB supports two helpful type checking system functions for null and undefined properties, both of which use the index:

  • IS_NULL– checks if a property value is null
  • You can also, of course, simply check if a value is null with an equality filter (example: SELECT * FROM c WHERE c.creationDate = null)
  • IS_DEFINED– checks if a property value is defined

In order for a filter expression to match an item, it must evaluate to true. In addition to false, all other values (including null or undefined) will exclude the item.

Here’s an example query:

SELECT *
FROM c
WHERE c.isRegistered = true

This example query will not include any items where isRegistered is null or undefined.

Understanding best practices

One of the biggest advantages of Azure Cosmos DB (and NoSQL in general) is simple support for unstructured data. If you have a Cosmos container that has items of varying structures or “schemas”, some items won’t contain the same properties as others. It is generally simpler and more efficient to simply not define a property than it is to both define a property and assign it a null value. The advantages of this approach are savings on storage size, ingestion costs, and simplified queries. A large number of null values in an item can be a signal that the data model could be further optimized.

The advantages of not explicitly defining null value properties is most obvious if you examine the RU charge of an item with a high number of null value properties.

#tips and tricks #azure cosmos db #null #undefined

PWA vs Native App: Which Is Better Option In 2021?

Every year, the world is expanding with the launch of new smartphones and other gadgets available in the market. According to Statista, more than 50% of the population will be using smartphones by the end of 2021.

Hence, businesses worldwide have understood the importance of smartphones and are joining the mobile industry by launching native apps.

Apart from native apps, progressive web apps is another technology that is gaining a lot of attention among businesses. Moreover, various leading companies worldwide have openly accepted PWA and built progressive web apps.

Now, the question arises, how is PWA different from the native apps? Read More

#pwa vs native #pwa vs native app #progressive web app vs native #progressive web app vs native app #pwa vs native app performance

akshay L

akshay L

1572939856

Hadoop vs Spark | Hadoop MapReduce vs Spark

In this video on Hadoop vs Spark you will understand about the top Big Data solutions used in the IT industry, and which one should you use for better performance. So in this Hadoop MapReduce vs Spark comparison some important parameters have been taken into consideration to tell you the difference between Hadoop and Spark also which one is preferred over the other in certain aspects in detail.

Why Hadoop is important

Big data hadoop is one of the best technological advances that is finding increased applications for big data and in a lot of industry domains. Data is being generated hugely in each and every industry domain and to process and distribute effectively hadoop is being deployed everywhere and in every industry.

#Hadoop vs Spark #Apache Spark vs Hadoop #Spark vs Hadoop #Difference Between Spark and Hadoop #Intellipaat