// Part 2, curry with placeholder
function curryWithPlaceholder(fn) {
// Don't use arrow function inside this
function curried(...args) {
// 1. Remove extra args
const sanitizedArgs = args.slice(0, fn.length);
<pre><code>// 2. check if there are placeholders
const hasPlaceholder = sanitizedArgs.some(arg =&gt; arg === curryWithPlaceholder.placeholder);

// 3. If no placeholder and args matches length then call
if (!hasPlaceholder &amp;&amp; sanitizedArgs.length === fn.length) {
 return fn.apply(this, sanitizedArgs);
}

// 4. We need to merge placeholders with actual values
return function nextCurried(...nextArgs) {
 return curried.apply(this, mergeArgs(sanitizedArgs, nextArgs))
}
</code></pre>
}
return curried;
function mergeArgs(oldArgs, newArgs) {
// oldArgs has placeholders
// for each placeholder, you pick from the newArgs
let result = [];
<pre><code>oldArgs.forEach(oldArg =&gt; {
 if (oldArg === curryWithPlaceholder.placeholder &amp;&amp; newArgs.length &gt; 0) {
 result.push(newArgs.shift());
 } else {
 result.push(oldArg);
 }
});
result = result.concat(newArgs);

return result;
</code></pre>
}
}
curryWithPlaceholder.placeholder = Symbol();

All tests ✅ Solution with explanation

This is a follow-up on 1. implement curry() please implement curry() which also supports placeholder. Here is an example const join = (a, b, c) => { r…