solved

src/queue/queue-data-structure.js

@@ -5,23 +5,32 @@ class Queue {
   }
 
   canEnqueue() {
-    // ... your code goes here
-  }
+    return this.queueControl.length < this.MAX_SIZE
+}
 
   isEmpty() {
-    // ... your code goes here
+    return this.queueControl.length === 0
   }
 
   enqueue(item) {
-    // ... your code goes here
+    if(this.canEnqueue()){
+      this.queueControl.push(item)
+      return this.queueControl
+    }
+    else{
+      throw new Error('QUEUE_OVERFLOW')
+    }
   }
 
   dequeue() {
-    // ... your code goes here
+    if(this.isEmpty()){
+      throw new Error('QUEUE_UNDERFLOW');
+    }
+    return this.queueControl.shift()
   }
 
   display() {
-    // ... your code goes here
+    return this.queueControl
   }  
 }
 

src/stack/stack-data-structure.js

@@ -5,23 +5,32 @@ class Stack {
   }
 
   canPush() {
-    // ... your code goes here
+    return this.stackControl.length < this.MAX_SIZE
   }
 
   isEmpty() {
-    // ... your code goes here
-  }
-
-  push(item) {
-    // ... your code goes here
+    return this.stackControl.length === 0
   }
+
+  push(item){
+    if(this.canPush()){
+      this.stackControl.push(item)
+      return this.stackControl
+    }
+    else {
+      throw new Error('STACK_OVERFLOW')
+    }
+}
 
   pop() {
-    // ... your code goes here
+    if(this.isEmpty()){
+      throw new Error('STACK_UNDERFLOW');
+    }
+    return this.stackControl.pop()
   }
 
   display() {
-    // ... your code goes here
+    return this.stackControl
   }  
 }