JSFiddle - React, Tailwind, and code Playground

by jfriend00

CSS

body {font-family: "Courier New";}

JavaScript

abcArr = [["A", 10], ["B", 20], ["A",30],["C",40]]

var items = {}, base, key;
for (var i = 0; i < abcArr.length; i++) {
    base = abcArr[i];
    key = base[0];
    if (!items[key]) {
        items[key] = 0;
    }
    items[key] += base[1];
}

// Now, generate new array
var outputArr = [], temp;
for (key in items) {
    temp = [key, items[key]]
    outputArr.push(temp);
}

// outputArr contains the result
document.body.innerHTML = JSON.stringify(outputArr);