Push Operation on Stack in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack array.

DSA Javascript

stack.push([1]);

Drag options to blanks, or click blank then click option'

Ashift

Bpop

Celement

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element instead of adding.

Using shift or unshift which work at the start of the array.

The push method adds the given element to the end of the stack array.

2fill in blank

medium

Complete the code to push the number 10 onto the stack array.

DSA Javascript

stack.push([1]);

Drag options to blanks, or click blank then click option'

Aten

B10

C"10"

D'10'

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around 10, which makes it a string instead of a number.

Using an undefined variable like ten.

To push the number 10, use the numeric value 10 without quotes.

3fill in blank

hard

Fix the error in the code to correctly push an element onto the stack.

DSA Javascript

stack.[1](element);

Drag options to blanks, or click blank then click option'

Apop

Bshift

Cremove

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element.

Using non-existent methods like remove.

The correct method to add an element to the stack is push. pop removes elements.

4fill in blank

hard

Fill both blanks to create a function that pushes a value onto the stack.

DSA Javascript

function pushToStack(stack, [1]) {
  stack.[2](value);
}

Drag options to blanks, or click blank then click option'

Avalue

Bpop

Cpush

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push.

Using inconsistent parameter names.

The function takes a parameter value and uses push to add it to the stack.

5fill in blank

hard

Fill all three blanks to push the uppercase version of the item onto the stack if it is a string.

DSA Javascript

function pushUppercase(stack, [1]) {
  if (typeof [2] === 'string') {
    stack.[3]([2].toUpperCase());
  }
}

Drag options to blanks, or click blank then click option'

Aitem

Bvalue

Cpush

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names causing errors.

Using pop instead of push.

The function uses value as the parameter and variable, and push to add the uppercase string to the stack.

Practice

1. What does the push operation do in a stack data structure?

easy

A. Checks if the stack is empty

B. Removes the top element from the stack

C. Returns the bottom element of the stack

D. Adds an element to the top of the stack

Solution

1. Step 1: Understand stack operations

   A stack follows Last In First Out (LIFO). The push operation adds an element on top.

2. Step 2: Identify the role of push

   It inserts a new element at the top, increasing stack size by one.

3. Final Answer:

   Adds an element to the top of the stack -> Option D

4. Quick Check:

   Push = Add top element [OK]

Hint: Push means add on top of stack [OK]

Common Mistakes:

• Confusing push with pop operation
• Thinking push removes elements
• Mixing stack with queue operations

2. Which of the following is the correct syntax to push an element 5 into a stack array named stack in JavaScript?

easy

A. stack.add(5);

B. stack.push(5);

C. push.stack(5);

D. stack.insert(5);

Solution

1. Step 1: Recall JavaScript array push syntax

   JavaScript arrays use push() method to add elements at the end.

2. Step 2: Match correct method call

   stack.push(5); correctly calls push on the array named stack.

3. Final Answer:

   stack.push(5); -> Option B

4. Quick Check:

   Array push method = stack.push(value) [OK]

Hint: Use arrayName.push(value) to add element [OK]

Common Mistakes:

• Using non-existent methods like add or insert
• Reversing method and object like push.stack()
• Forgetting parentheses after push

3. What will be the output after executing the following code?

const stack = [];
stack.push(10);
stack.push(20);
stack.push(30);
console.log(stack);

medium

A. [10, 20]

B. [30, 20, 10]

C. [10, 20, 30]

D. Error: push is not a function

Solution

1. Step 1: Trace push operations on empty stack

   Initially stack is empty []. After push(10), stack = [10]. After push(20), stack = [10, 20]. After push(30), stack = [10, 20, 30].

2. Step 2: Understand console.log output

   Logging stack prints the array as is: [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option C

4. Quick Check:

   Push adds at end, so stack = [10,20,30] [OK]

Hint: Push adds at end, array grows left to right [OK]

Common Mistakes:

• Assuming push adds at start (top as front)
• Confusing stack order with queue
• Expecting reversed array output

4. Identify the error in the following code snippet that tries to push an element into a stack:

let stack = 5;
stack.push(10);

medium

A. stack is not an array, so push method is undefined

B. push method requires two arguments

C. stack.push should be stack.add

D. No error, code runs fine

Solution

1. Step 1: Check variable type of stack

   stack is assigned number 5, not an array. Numbers do not have push method.

2. Step 2: Understand push method applicability

   push is an array method. Calling push on a number causes error: push is not a function.

3. Final Answer:

   stack is not an array, so push method is undefined -> Option A

4. Quick Check:

   push only works on arrays [OK]

Hint: Only arrays have push method [OK]

Common Mistakes:

• Assuming push works on numbers
• Thinking push needs multiple arguments
• Confusing push with add method

5. Given a stack implemented as an array, how would you push multiple elements [1, 2, 3] onto it so that 3 is on top after all pushes?
Choose the correct code snippet.

hard

A. stack.push(1); stack.push(2); stack.push(3);

B. stack.push(3); stack.push(2); stack.push(1);

C. stack.push([1, 2, 3]);

D. stack = [1, 2, 3];

Solution

1. Step 1: Understand push order for stack

   Push adds elements on top. To have 3 on top, push 1 first, then 2, then 3.

2. Step 2: Analyze options

   Sequential pushes of 1 then 2 then 3 add elements individually with 3 on top. Pushing [1,2,3] adds a single array element with [1,2,3] on top. Reverse pushes put 1 on top. Assignment replaces the stack entirely.

3. Final Answer:

   stack.push(1); stack.push(2); stack.push(3); -> Option A

4. Quick Check:

   Push in order to have last element on top [OK]

Hint: Push elements in order, last pushed is top [OK]

Common Mistakes:

• Pushing array [1,2,3] as single element
• Pushing in reverse order
• Replacing stack instead of pushing