<pre class="shiki github-dark shaku"><code>/** * @param {Thunk} thunk * @return {Thunk} */function flattenThunk(thunk) { // your code here return function(cb) { const runThunk = (thunk) =&gt; { return new Promise((resolve,reject) =&gt; { thunk((err, data) =&gt; { if (err) { reject(err) } else { if (typeof data === 'function') { resolve(runThunk(data)) } else { resolve(data); } } }) }) } runThunk(thunk).then(data =&gt; cb(undefined, data)).catch(err =&gt; cb(err, undefined)) }}</code></pre>

promise解法。定义一个运行Thunk的函数，返回promise，如果data是函数，递归调用函数，否则resolve data,有报错直接reject

Suppose we have a Callback type type Callback = (error: Error, result: any | Thunk) => void A Thunk is a function that take a Callback as parameter ty…