JSFiddle - React, Tailwind, and code Playground

JavaScript

var responseData = [
  {deviceType: "Smartphone", deviceCount: 14},
  {deviceType: "Tablet", deviceCount: 11},
  {deviceType: "Notebook", deviceCount: 3},
  {deviceType: "Desktop", deviceCount: 2},
  {deviceType: "Smartphone", deviceCount: 1},
  {deviceType: "Tablet", deviceCount: 10},
  {deviceType: "Notebook", deviceCount: 30},
  {deviceType: "Desktop", deviceCount: 20}
];

function dataMapper(responseData){
  var series = {};
  if(responseData && responseData.length){
  responseData.forEach(function(element){
       series[element.deviceType] = Number.isInteger(series[element.deviceType]) ? series[element.deviceType] + element.deviceCount : element.deviceCount
    });
  }
  var tmp = []
  for (var i in series) {
    tmp.push({deviceType: i, deviceCount: series[i]})
  }
  return tmp
}

console.log(dataMapper(responseData))