JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {
    a: [1,2,3],
    b: [4,5,6],
    c: [7,8,9]
}

var end = [];

for (var k in obj) {
    for (var i = 0, l = obj[k].length; i < l; i++) {
        end.push(obj[k][i])
    }
}
console.log(end)

var end = [];

for (var k in obj) {
  end.push(obj[k])
}

var merged = [];
merged = merged.concat.apply(merged, end);

console.log(merged)