Fixed point in JavaScript

kleene.js

// s-m-n
const s = "(f, x) => `y => (${f})(${x}, y)`";

// fixed point
const e = q => {
    const n = `(x, y) => (${q})((${s})(x, x), y)`;
    const p = eval(`(${s})(n, n)`);
    return `(${p})(0)`;
};

// test
const q = "(x, y) => x";
const fix = e(q);
eval(`(${q})(${fix})`) === eval(`${fix}`);