add js Solution for 278;

Author: limbowandering

solution/278.First Bad Version/Solution.js

@@ -0,0 +1,34 @@
+/**
+ * Definition for isBadVersion()
+ * 
+ * @param {integer} version number
+ * @return {boolean} whether the version is bad
+ * isBadVersion = function(version) {
+ *     ...
+ * };
+ */
+
+/**
+ * @param {function} isBadVersion()
+ * @return {function}
+ */
+const solution = function(isBadVersion) {
+  /**
+   * @param {integer} n Total versions
+   * @return {integer} The first bad version
+   */
+  return function(n) {
+      if(n === 1) return n;
+      let left = 1, right = n;
+      while(left < right){
+        let mid = left + Math.floor((right-left)/2);
+        if(isBadVersion(mid)){
+          if(mid === left) return mid;
+          else right = mid;
+        }else{
+          if(isBadVersion(mid+1)) return mid+1;
+          else left = mid + 1;
+        }
+      }
+  };
+};