JSFiddle - React, Tailwind, and code Playground

JavaScript

function map (arr, func) {
    var i = arr.length;
    arr = arr.slice();
    while (i--) arr[i] = func(arr[i]);
    return arr;
}

var object = function (key, text) {
    this.key = key;
    this.text = text;
};

var objArray = [];
objArray[0] = new object('key1','blank');
objArray[1] = new object('key2','exampletext');
objArray[2] = new object('key3','moretext');

var keyArray = map(objArray, function (obj) { return obj.key; });

document.body.innerText = JSON.stringify(keyArray);