diff --git a/index.html b/index.html
index 3fab1ac7..74d54a96 100644
--- a/index.html
+++ b/index.html
@@ -27,6 +27,7 @@ <h2>Stack</h2>
               placeholder="Add element to the stack"
             />
           </div>
+
           <button
             id="add-stack"
             type="button"
@@ -34,6 +35,7 @@ <h2>Stack</h2>
           >
             Add to stack
           </button>
+ 
           <button
             id="take-stack"
             type="button"
@@ -41,12 +43,14 @@ <h2>Stack</h2>
           >
             Remove from stack
           </button>
+
           <div class="stack-container" id="stack-container">
             <div class="warning-top alert alert-danger"></div>
             <ul id="stack-list" class="list-stack"></ul>
             <div class="warning-bottom alert alert-danger"></div>
           </div>
         </div>
+
         <div class="col-sm-1"></div>
 
         <div class="col-sm-7">
@@ -59,6 +63,7 @@ <h2>Queue</h2>
               placeholder="Add element to the queue"
             />
           </div>
+
           <button
             id="add-queue"
             type="button"
@@ -66,6 +71,7 @@ <h2>Queue</h2>
           >
             Add to queue
           </button>
+
           <button
             id="take-queue"
             type="button"
diff --git a/src/queue/queue-data-structure.js b/src/queue/queue-data-structure.js
index 98ac0fd0..209b10eb 100644
--- a/src/queue/queue-data-structure.js
+++ b/src/queue/queue-data-structure.js
@@ -6,22 +6,34 @@ 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() === false){
+      throw new Error('QUEUE_OVERFLOW')
+    }
+    this.queueControl.push(item);
+    return this.queueControl;
   }
 
   dequeue() {
     // ... your code goes here
+    if(this.isEmpty() === true){
+      throw new Error('QUEUE_UNDERFLOW')
+    }
+    return this.queueControl.shift();
   }
 
   display() {
     // ... your code goes here
+    return this.queueControl;
   }  
 }
 
diff --git a/src/stack/stack-data-structure.js b/src/stack/stack-data-structure.js
index 1106f6f3..b48b9f0b 100644
--- a/src/stack/stack-data-structure.js
+++ b/src/stack/stack-data-structure.js
@@ -6,22 +6,40 @@ class Stack {
 
   canPush() {
     // ... your code goes here
+    if(this.stackControl.length < this.MAX_SIZE){
+      return true;
+    } else {
+      return false;
+    }
   }
 
   isEmpty() {
     // ... your code goes here
-  }
+    return this.stackControl.length === 0;
+    }
 
   push(item) {
     // ... your code goes here
+    if(this.canPush() === true){
+      this.stackControl.push(item);
+      return this.stackControl;
+    } else {
+      throw new Error("STACK_OVERFLOW")
+    }
   }
 
   pop() {
     // ... your code goes here
+    if (this.isEmpty() === false) {
+      return this.stackControl.pop();
+    } else {
+      throw new Error("STACK_UNDERFLOW");
+    }
   }
 
   display() {
     // ... your code goes here
+    return this.stackControl;
   }  
 }