JSFiddle - React, Tailwind, and code Playground

JavaScript

var array = [
    {
        "foo": "piet",
        "doo": "aaa111"
    },
    {
        "foo": "piet",
        "doo": "bbb222"
    },
    {
        "foo": "jan",
        "doo": "ccc333"
    },
    {
        "foo": "henk",
        "doo": "ddd444"
    },
    {
        "foo": "henk",
        "doo": "fff555"
    }
];

var newarray = array.filter((item, index, self) => self.findIndex(t => t.foo === item.foo) === index)

console.log(newarray)