JSFiddle - React, Tailwind, and code Playground

JavaScript

var ptr = (function () {
    var ptr = "(" + String(function (value) {
    if (value === void 0) return upvalue;
    else upvalue = value;
}) + ")";

    return function (upvalue) {
        return ptr.replace(/upvalue/g, upvalue);
    };
}());

function swap(xptr, yptr) {
    var t = xptr();
    xptr(yptr());
    yptr(t);
}

var x = 2;
var y = 3;

alert([x, y]);
swap(eval(ptr("x")), eval(ptr("y")));
alert([x, y]);