JSFiddle - React, Tailwind, and code Playground

by ciju

JavaScript

var Y = function (fn) {
    return (function (g) {
        return g(g);
    })(function (h) {
        return fn(function (n) {
            return h(h)(n);
        });
    });
};
var sum = function (f) {
    return function (n) {
        return n === 1 ? 1 : n + f(n - 1);
    };
};
console.assert(Y(sum)(5) === 15);