<pre class="shiki github-dark shaku"><code>/** * @param {number} num */function sum(num) { const func = function (num2) { return sum(num + num2); } func.valueOf = () =&gt; num return func;}</code></pre>

Easiest solution

Create a sum(), which makes following possible const sum1 = sum(1)sum1(2) == 3 // truesum1(3) == 4 // truesum(1)(2)(3) == 6 // truesum(5)(-1)(2) == 6 …