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curriculum/challenges/english/10-coding-interview-prep/data-structures/create-a-stack-class.md

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+---
+id: 587d8250367417b2b2512c5f
+title: Create a Stack Class
+challengeType: 1
+forumTopicId: 301633
+---
+
+## Description
+<section id='description'>
+
+In the last section, we talked about what a stack is and how we can use an array to represent a stack. In this section, we will be creating our own stack class.
+Although you can use arrays to create stacks, sometimes it is best to limit the amount of control we have with our stacks.
+Apart from the <code>push</code> and <code>pop</code> method, stacks have other useful methods. Let's add a <code>peek</code>, <code>isEmpty</code>, and <code>clear</code> method to our stack class.
+</section>
+
+## Instructions
+<section id='instructions'>
+
+Write a <code>push</code> method that pushes an element to the top of the stack, a <code>pop</code> method that removes and returns the element on the top of the stack, a <code>peek</code> method that looks at the top element in the stack, an <code>isEmpty</code> method that checks if the stack is empty, and a <code>clear</code> method that removes all elements from the stack.
+Normally stacks don't have this, but we've added a <code>print</code> helper method that console logs the collection.
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: Your <code>Stack</code> class should have a <code>push</code> method.
+    testString: assert((function(){var test = new Stack(); return (typeof test.push === 'function')}()));
+  - text: Your <code>Stack</code> class should have a <code>pop</code> method.
+    testString: assert((function(){var test = new Stack(); return (typeof test.pop === 'function')}()));
+  - text: Your <code>Stack</code> class should have a <code>peek</code> method.
+    testString: assert((function(){var test = new Stack(); return (typeof test.peek === 'function')}()));
+  - text: Your <code>Stack</code> class should have a <code>isEmpty</code> method.
+    testString: assert((function(){var test = new Stack(); return (typeof test.isEmpty === 'function')}()));
+  - text: Your <code>Stack</code> class should have a <code>clear</code> method.
+    testString: assert((function(){var test = new Stack(); return (typeof test.clear === 'function')}()));
+  - text: The <code>peek</code> method should return the top element of the stack
+    testString: assert((function(){var test = new Stack();  test.push('CS50'); return (test.peek() === 'CS50')}()));
+  - text: The <code>pop</code> method should remove and return the top element of the stack
+    testString: assert((function(){var test = new Stack(); test.push('CS50'); return (test.pop() === 'CS50');}()));
+  - text: The <code>isEmpty</code> method should return true if a stack does not contain any elements
+    testString: assert((function(){var test = new Stack(); return test.isEmpty()}()));
+  - text: The <code>clear</code> method should remove all element from the stack
+    testString: assert((function(){var test = new Stack();  test.push('CS50'); test.clear(); return (test.isEmpty())}()));
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function Stack() {
+  var collection = [];
+  this.print = function() {
+    console.log(collection);
+  };
+  // Only change code below this line
+
+  // Only change code above this line
+}
+```
+
+</div>
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+class Stack {
+  constructor() {
+    this.collection = [];
+  }
+  print() {
+    console.log(this.collection);
+  }
+  push(val) {
+    this.collection.push(val);
+  }
+  pop() {
+    return this.collection.pop();
+  }
+  peek() {
+    return this.collection[this.collection.length - 1];
+  }
+  isEmpty() {
+    return this.collection.length === 0;
+  }
+  clear() {
+    return (this.collection.length = 0);
+  }
+}
+```
+
+</section>