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

not sure

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 …