JSFiddle - React, Tailwind, and code Playground

JavaScript

var items = {
    a: ['STRAWBERRY', 'PEANUT'],
    b: ['John', 'Doe', 'Scarface'],
    c: ['Circle', 'Square', 'Triangle', 'Rectangle'],
};

function getLength (obj) {
    var length = 0;
    for (var key in obj) {
        if (obj.hasOwnProperty(key)) {
            if (obj[key].length > length) {
                length = obj[key].length;
            }
        }
    }
    return length;
}

function merge () {
    var newArray = [];
    var length = getLength(items);
    console.log(length);
    var index = 0;
    for ( ; index < length; index++) {
    	for (var key in items) {
            if (items[key][index]) {
                newArray.push(items[key][index]);
            }
        }
    }
    console.log(newArray)
}

merge();