JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li id="0"></li>
    <li id="213"></li>
    <li id="324"></li>
    <li id="764"></li>
</ul>

JavaScript

var map = $("ul").children().map(function(i, el) {
    return el.id;
})

console.log(Array.prototype.slice.call(map).join(":")); // 0:213:324:764 
console.log(map.join(":")); //error