• Origin story: In 1993, IBM launched the first-ever known smartphone which had apps like a contact book, calendar, world clock, and calculator.
• Widely popular:As of 2019, according to Business of apps, there are about 26.4 million app developers in the world. Out of these, 6 million work on Android development only.
• Width of knowledge: A App developer is a programmer with knowledge across all layers of an application.
  1. Presentation Layer: The front-end of an application built using programming languages like HTML, CSS, JavaScript, jQuery, and various JavaScript libraries such as Foundation, AngularJS, Backbone, Ember.js, and React JS.
  2. Logic Layer: The backend of an application built using programming languages like Java, PHP, .Net, Ruby, and Python.
  3. Data Layer: A sub-group of the logic layer that deals with how data is created, modified, read, managed, and deleted using databases like SQL Server, MySQL, Oracle, and PostgreSQL.

• Economical: By using applications, there is less human work and everything is converted into a computerized format, therefore saving time and money.
• Higher ROI: Apps effectively helps in engaging customers, leading to higher ROI and growth of the business

These are some of the tools commonly used by app developers:

1. Titanium SDK

The Titanium SDK is a software development kit using which users can develop cross-platform applications. It is an open-source tool that allows writing the code in JavaScript and running as native apps across platforms.

2. Kobiton

This tool provides options for manual and automated testing of mobile applications. Thanks to it, the testing and delivery of the applications are sped up.

3. Qt

Qt is a cross-platform mobile app development tool. It allows for creating the graphical user interface and cross-platform apps. Users can then run these apps on a number of software and hardware platforms including Windows, Linux, Android, and macOS.

4. TensorFlow

In case an app developer intends to integrate AI/ML in their application, TensorFlow is the tool for that. This is an open-source, free collection of modules that is useful for making modules using JavaScript and Python.

5. Apache Cordova

A mobile app development framework, Apache Cordova is an open-source tool using which app developers can build hybrid apps. Languages like HTML, CSS, and JSS can be used rather than platform-specific tech.

Below are some key points that we at Flexiple have learned through trial and error - a process of filtering through over 15,000 developers. You can use these in your process to hire app developers.

• Years of software development experience: Be specific about the technology you’re looking for and the number of years of experience needed. A proxy to years of experience can be the number of production-level apps worked on.
• Expertise in a specific language: All languages have their peculiarities and nuances. While good App developers can pick up other languages, it’s a plus point to hire a developer who already has expertise in it.
• Type of products built in the past: Based on the type of product you are trying to build - social network, SAAS product, etc. - you can prioritize certain developers over others.
• Exposure to specific industries: Developers who have built products in certain industries will already know key aspects of laying the foundation for a great product and will be able to predict possible problems.
• Experience working remotely: A developer with past remote work experience is an added advantage as they would have first-hand experience of everything - right from how contracts work to streamlined communication, as well as timelines and deliverables.
• Strong communication: An essential thing to look at when hiring a freelancer is excellent communication skills. Since all the interaction happens online, a freelancer should be able to effectively communicate to ensure a streamlined execution of all work.

Now that you have made a quality JD, it can still be tricky to evaluate the skills of your applicants when you hire app developers. To help you with that, we have created a pool of questions that a good App developer should be comfortable with.

It is important to note that the ability to answer these questions doesn't imply that you have a top quality candidate. But it definitely is a big step in that direction.

To help you navigate through these questions, we’ve categorized the interview questions in 3 parts:

A. Basic concepts: Includes all basic concepts used across languages. This section will give you an understanding of how strong their programming foundation is.

B. Advanced concepts: Includes all concepts that someone with higher expertise should know.

C. DS/Algorithm questions: To test the logical capability of the candidate.

A. Basic concepts

What are the advantages of using REST web services?

Listed below are a few advantages of using REST web services:

1. - Rest is a simple, lightweight, and fast protocol
2. - The learning curve is small as it uses the HTTP protocol
3. - Since the resources are decoupled the content can be accessed in numerous formats (HTML, Text, JSON, PDF, etc)

Why are doctypes used in HTML?

HTML Doctypes are not elements or tags but rather a document type declaration. This document is used to tell the web browser the HTML version used or about any other markup language that is used on the current page.

These doctypes must be added before the <html> tags. The following code is used to declare it.

< !DOCTYPE html >

B. Advanced concepts

Describe sessionStorage, localStorage, and cookie.

Session Storage - As the name suggests, this data is stored until the session or tab is closed, however, it is not cleared during reloads. This data remains on the client-side and cannot be transferred to the server.

Local Storage - This data is stored on the client's computer. This data has no expiration, however, it is limited only to string data. Local data can be accessed using Javascript and HTML but cannot be transferred to the server end. Although local storage data does not have an expiration date it can be cleared by the user.

Cookies - Cookies sent back to the server-side and hence the size must be less than 4KB. The data is sent back when a subsequent XHR request is made. Although they are meant for server-side reading they can be accessed on the client-side as well.

What are the various ways to get elements from the DOM?

These are the common methods used to get an element from the DOM:

1. getElementById
2. getElementsByClassName
3. getElementsByTagName
4. querySelector
5. querySelectorAll

C. Data Structure/ Algorithm

1. Write a Java Program to find whether a string or number is palindrome or not.

import java.util.Scanner;
public class Palindrome {
    public static void main (String[] args) {
        String original, reverse = "";
 Scanner in = new Scanner(System.in);
       int length;
        System.out.println("Enter a number or a string");
        original = in.nextLine();
        length = original.length();
        for (int i =length -1; i>;=0; i--) {
            reverse = reverse + original.charAt(i);
        }
        System.out.println("The reverse is: " +reverse);

        if(original.equals(reverse))
            System.out.println("The string is a palindrome");
        else
            System.out.println("The stringis not a palindrome");

    }
}

Output:
For String- Enter a number or a string
sam
The reverse is: mas
The string is not a palindrome

For Number-Enter a number or a string
99
The reverse is: 99
The number is a palindrome 

2.What will the output of the following code be?

$x = 2
$y = 4
$z = 6
if($z > $y > $x) {
    echo “true”;
}else{
    echo “false”;
}

The answer is False. It may look like the output can be true because 6 > 4 > 2 is true, but PHP evaluates $z > $y 
first, which returns a boolean value of 1 or true. This value (true or 1) is compared
to the next integer in the chain, bool(1) > $z, which will result in NULL and echo “false.”

That is everything you need to know about hiring a freelance App developer. As discussed, it isn't easy to find a quality freelance App developer but this guide makes the process easier for you. To offload the entire hiring process, reach out to us at Flexiple. We've designed a high-quality, 6-step screening process to find the top 1%, freelance developers. You can find the best freelance App developers here. We've already served over a hundred clients, earning great reviews for the quality of service.

Lastly, to quickly summarize it for you:

• Note your project requirements and hire accordingly. Do not go for the lowest or the highest-paid developer.
• Don’t hire without vetting- consider asking questions right from the basics to advanced to logical questions.
• Look for companies like Flexiple that help you find the perfect fit.

That's a wrap on the info you need to hire app developers. Happy hiring! :)