<pre class="shiki github-dark shaku"><code>// This is a JavaScript coding problem from BFE.dev /* type IsBad = (version: number) =&gt; boolean *//** * @param {IsBad} isBad */function firstBadVersion(isBad) { // firstBadVersion receive a check function isBad // and should return a closure which accepts a version number(integer) return (version) =&gt; { // write your code to return the first bad version // if none found, return -1 let scopeStartPointer = 0; let scopeEndPointer = version; while (scopeStartPointer &lt;= scopeEndPointer) { const middle = Math.floor((scopeStartPointer + scopeEndPointer) / 2); if (isBad(middle)) { scopeEndPointer = middle - 1; } else { scopeStartPointer = middle + 1; } } return isBad(scopeStartPointer) ? scopeStartPointer : -1; }}</code></pre>