groupingByInJavaScript.js

var arr = [ 
{ name: "A", value: 10 },
{ name: "B", value: 20 },
{ name: "C", value: 30 },
{ name: "A", value: 40 },
{ name: "B", value: 50 },
{ name: "C", value: 60 }];

var accumulated = arr.reduce(function(accumulator, element) {
var currentValue = accumulator[element.name];

if(currentValue !== undefined) {
  accumulator[element.name] = currentValue + element.value;
}
else {
  accumulator[element.name] = element.value;
}
return accumulator;
}, {});

var result = Object.keys(accumulated).map(function(k) {return {name: k, value: accumulated[k]}})