JSFiddle - React, Tailwind, and code Playground

JavaScript

var allList = [{firstName: "Frank", lastName: "Tester"}, {firstName: "List", lastName: "Tester 2"}];

function generate(list) {
    var out = '';
    
    for (var i in list) {
        var rec = list[i];
        var row = [];
        
        for (var field in rec) {
            row.push(field + ': ' + rec[field]);
        }
        
        out += "<li>" + row.join(', ') + "</li>";
    }
   
    return "<ul>" + out + "</ul>";
}

document.write(generate(allList));