Added JS solution of uncompress-string

problem/uncompress-string_en.md

@@ -1,4 +1,29 @@
-
-There is no solution yet.
-
-Would you like to [contribute to the solution](https://github.com/BFEdev/BFE.dev-solutions/blob/main/problem/uncompress-string_en.md)? [Contribute guideline](https://github.com/BFEdev/BFE.dev-solutions#how-to-contribute)
+function uncompress(str) {
+  let curNum=0, curStr='',stack=[]
+  for(let i=0;i<str.length;++i){
+    // If it is a digit
+    if(!isNaN(parseInt(str[i]))){
+      if(i>0 && !isNaN(parseInt(str[i-1]))){
+        curNum = curNum*10+parseInt(str[i])
+      } else {
+        curNum=parseInt(str[i])
+      }
+    }
+    //If it is opening brancket
+    else if(str[i]==='('){
+      stack.push({curNum,curStr});
+      curNum=0;
+      curStr=''
+    }
+    //If it is closing brancket
+    else if(str[i]===')'){
+      let element = stack.pop();
+      curStr = element.curStr + curStr.repeat(element.curNum)
+    }
+    //If it is alphabets
+    else {
+      curStr+=str[i]
+    }
+  }
+  return curStr
+}