JSFiddle - React, Tailwind, and code Playground

JavaScript

const list = [{
    x: 'SomeName-1',
    value: 2
  },
  {
    x: 'SomeName-2',
    value: 3
  },
  {
    x: 'SomeName-1',
    value: 5
  },
  {
    x: 'SomeName-2',
    value: 8
  },
  {
    x: 'SomeName-1',
    value: 1
  },
  {
    x: 'SomeName-3',
    value: 4
}];

const newList = list.reduce((items, item) => {
	const {x, value} = item;
  const itemIndex = items.findIndex(item => item.x === x)
  if(itemIndex === -1){
  	items.push({
    	x, value
    });
  } else {
  	items[itemIndex].value += value;
  }
  
  return items;
}, []);

console.log(newList);