Petar Simic, Developer in Belgrade, Serbia
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Petar Simic

Verified Expert  in Engineering

Single-page Applications (SPA) Developer

Belgrade, Serbia
Toptal Member Since
November 18, 2014

Petar has extensive experience in developing web applications and custom JavaScript libraries. He is a highly responsible team player and a passionate coder who is always looking for challenge and perfection. He is very good at resolving user interface problems and interaction, and prides himself on his tenacity in solution building.



Preferred Environment

Visual Studio Code (VS Code), Git, Ubuntu, Figma

The most amazing...

...thing I've created is a dynamic web application that allows users to create multiple desktops with widgets for different data types and a social function.

Work Experience

JavaScript/Angular Developer

2015 - PRESENT
Online Freelance Agency
  • Created a reusable data manager for easier manipulation of response objects from any API configuration. Also supports deep binding directly on model structure so for return it provides first level data for fast performance reading and writing.
  • Created a reusable parser that can manage a number of viewable items for any platform and/or view type (list, grid, etc.) with a simple configuration file. Also supporting auto scrolling and auto pulling of data from the API.
Technologies: CSS3, HTML5, AngularJS, Angular, JavaScript

Web Developer

2014 - PRESENT
Toptal Clients
  • Developed custom and specific web applications based on client documentation and needs.
  • Built responsive web pages following client requests and design mocks.
  • Collaborated with teams on projects and plans from collecting and writing documentation up to UX improvements and specific logical solutions following best practices.
  • Developed and organized projects and roles. Handled core architectural solutions and the development planning process including Agile Methodology.
  • Honed a keen eye for the details and from the experience over the years. I was trying to point out and solve possible UI/UX issues and extend the experience with every new project or challenge.
Technologies: CSS, HTML, Angular, AngularJS

Senior Full-stack Developer

2019 - 2022
  • Developed many specific modules for querying and UI rendering, using Elasticsearch, Node.js, Gatsby, React, HTML, and CSS.
  • Tracked and fixed issues in Elasticsearch queries, including optimizations and boosting query response time.
  • Planned teamwork, organized tasks and bugs owners, tracked team progress and support, and debugged blockers.
Technologies: Node.js, React, SCSS, HTML, Gatsby, Next.js, Jest, Elastic

Developer and Team Lead

2017 - 2019
  • Managed and organized the team, interviewed new candidates. Organized training sessions to improve coding.
  • Wrote documentation and specifications for new features.
  • Created reusable components that are and can be used across the system. Components determine what the content type is and display that content as a tooltip or modal window.
  • Created migration files for seeding data and manipulating with column names and value types, using Sequelize.
  • Refactored existing components covered with tests on both sides using Angular and Node.
  • Built new UI components from the provided designs from internal company or client mocks created.
Technologies: MySQL, Node.js, Angular


2014 - 2015
Pure Blue Software. LLC.
  • Developed an application that tracks and organizes employees. Organizers are enabled to add and change each individual employee plan by interacting on the calendar. Similar to Google Calendar.
  • In order to get the best performance I had to develop custom calendar component and custom drag-n-drop component for setting employee tasks. App had to handle overlaping and organization of UI when multiple tasks are on calendar.
  • Developed different user roles and views of the calendar and employee tasks.
Technologies: Responsive Web Design (RWD), Graphic Design, Adobe Photoshop, Data Modeling, JavaScript, jQuery

Web Developer

2014 - 2015
Tailor and Made
  • Built websites with full cross-browsing compatibility from all desktop browsers on Windows, Linux, and Mac to all mobile and tablet platforms.
  • Created a few quick-loading "single page" static websites which use different types of libraries and components that are optimized to work from IE8+.
  • Development of custom css3 animations for websites.
Technologies: CSS3, HTML5, JavaScript

JavaScript/PHP Developer

2014 - 2015
Full Dream Solutions
  • Created data communication between Unity3D (mobile, web) and different type of APIs like Shopify.
  • Built a MySQL DB with RESTful APIs for a multiplayer game.
  • Programmed a reusable JSON parser in C# that manages particular types of data as requested on one gaming product.
Technologies: MySQL, JavaScript

Lead Front-end Engineer and Team Lead

2011 - 2014
  • Collaborated to create a custom JavaScript MVC framework that saves implementation time and spares developers the hassle of working with HTML structures by managing everything over a controller setup and hierarchy of controllers.
  • Created hundreds of different widgets built from ten simple templates. All of them are specially made to be implemented modularly and give the developer an opportunity to create new widgets with a minimum of testing.
  • Planned and researched UI on most projects to find the best optimal solution for all three sides, including designers, developers, and users, so building projects with a streamlined user interface will work more quickly in the future.
  • Organized team members and managed code quality control.
  • Took full responsibility for the system as a whole and performed training of new staff.
Technologies: XML, Git, CSS3, CSS, HTML5, HTML, JavaScript

Web Developer

2010 - 2011
  • Developed a static website with a Flash introduction page.
  • Implemented multi-language support.
  • Conducted SEO optimization.
Technologies: CSS, HTML, JavaScript

Volunteer Java, JavaScript, and Delphi Programmer

2009 - 2009
Red Cross
  • Created an MDI application in Java and Delphi for managing data.
  • Built a generic application that is able to build independently and manage user interfaces based on database XML schematics.
  • Supported offline (local) and online (server) data storage with auto-synchronization when the app connects to the internet.
Technologies: Microsoft SQL Server, Microsoft Access, RAD Studio, Delphi, Java

Online Directory

An AngularJS-based web application for an online directory of a wide range of businesses that can be reviewed and checked by anyone.

This application supports profile creation, reviews, and comments on different businesses. Users gain different levels of badges based on the experiences they shared and are also allowed to upload photos and bookmark favorite businesses. Sharing is supported on all major applications. The application is compatible with all platforms including mobile devices and old browsers.

Earthquake Simulator
An AngularJS-based web application for creating real-time simulations in browser, with data provided from seismic sensors and drawing waves and effect on map using ArcGIS API. For calculation, it uses Graham scan (algorithm) in order to get more realistic areas that were affected by an earthquake.

Regex Generator

An AngularJS-based web application, a generator for manipulating words and sentences in order to create funny letters from a serious business one. With the simple configuration file and list of words that will be replaced, the generator that was built in code is reusable and simple to modify. Also, the admin is able to modify the percent of modification that can be made by the generator.

Interactive Organizer

Built in pure JavaScript to get the best performance, this website application manages the daily/weekly/monthly plan of each worker and client. This application calculates available hours and pause offsets for each worker based on previous and next tasks that are already scheduled. Simple drag-n-drop brings each task to the calendar view, automatically applying new offsets for start and end time in the defined working hour scope.

Virtual Boards/Item Manager

A website application, built on a customized Backbone library, that allows users to create boards and use each of them for creating and gathering different types of items from the cloud, with Dropbox and Google Drive, from stores like Amazon, music services like Soundcloud, and user desktops. I was involved in the UX/UI development and integration. My responsibility was to implement core architecture.


An online TV channel that provides custom videos for one particular sport. I worked on the dynamic elements of the application responsible for the video player, the relationships between galleries and players, and communication with the back-end. The main gallery has different states of rolling "currently playing" video on the first position in the first row from the second row.


A system for an aviation company that required three completely independent content management systems and two websites for customers and employees. I worked on one of the content management systems built for planning plane routes, registering routes with airports, calculating expenses, and finding the best and the cheapest routes for traveling. My responsibility was to organize the front-end core architecture. I also developed major functionality and coordinated team efforts.


Three projects related to annual reports and promotion for two large global corporations, with a goal of covering a wide area of platforms, browsers, and media sizes with a static, single page which had to be fully resizable and quick loading. Each project has about seven pages arranged in one line on the Body element, with the active one in focus and the others locked to the side like stacked pieces of paper.


An application for gift sales. The company has a wide range of clients and customers and gives clients an opportunity to gain more sales for their products worldwide without pushing customers to go to stores. Everything is done via online payments and vouchers. My work was based on the content management system for this application, building a fully customized editor that gives clients the chance to create their own promotions and publish them independently of the main system.


An application for a cinema advertising company that provides premium marketing and media solutions for advertisers and comprehensive representation of the cinema's advertising partners. I implemented the website application giving customers an opportunity to register and review/rate movies and to take part in the weekly quiz to get free tickets for the latest movies. The user is able to search movies and check theater locations by proximity to a zip code.


An Android application for creating custom bracelets in 3D with ordering and payment mechanisms. I implemented a Shopify API and PHP RESTful service that provides all the data from the Shopify store server related to products and prices, as well as communication with another server where the 3D models and other application data is stored.

Cost Plus Drugs
I was a software engineer on this project. My responsibility was the development of new features, components, and optimization. Besides React on the front end, I had to develop, maintain, and support the development of new features on the back end with Node.js and GraphQL.


JavaScript, CSS3, XML, HTML, CSS, HTML5, TypeScript, GraphQL, TypeScript 2, SQL, Sass, Less, SCSS


Angular, AngularJS, Next.js, Jest


Git, Figma, Webpack, Elastic, Adobe Photoshop


Responsive Layout, REST, Responsive Web Design (RWD), Object-oriented Programming (OOP), Agile Software Development, Unit Testing


Visual Studio Code (VS Code)


Elasticsearch, MySQL


Responsive UI, Responsive Web Apps, User Interface (UI), Single-page Applications (SPA), Content Management Systems (CMS), Web Standards, Quick Study, User Experience (UX), Dom Manipulation, Gatsby, Graphic Design, Data Modeling


React, Preact, Node.js, jQuery

2012 - 2016

Bachelor's Degree in Software Engineering

Metropolitan University - Belgrade