<pre class="shiki github-dark shaku"><code>/** * @param {number} num */function sum(a) { const fn = (b) =&gt; sum(a + b); fn[Symbol.toPrimitive] = () =&gt; a; return fn;}function sum1(a) { const fn = (b) =&gt; sum1(a + b); fn.toString = () =&gt; a; return fn;}function sum2(a) { const fn = (b) =&gt; sum2(a + b); fn.valueOf = () =&gt; a; return fn;}</code></pre>

3 Possible EXAMPLES

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 …