--update: aded Stack

Author: ashokdey

src/_DataStructures_/Queue/Queue.test.js

@@ -20,8 +20,8 @@ describe('Data Structure : Queue', () => {
     it('Should remove() an element from the queue', () => {
       queue.add(2);
       queue.add(3);
-      queue.remove();
 
+      expect(queue.remove()).toEqual(2);
       expect(queue.data).toEqual([3]);
     });
 

src/_DataStructures_/Stack/Stack.test.js

@@ -0,0 +1,57 @@
+const Stack = require('.');
+
+describe('Data Structure : Stack', () => {
+  it('Should be class', () => {
+    expect(typeof Stack.prototype.constructor).toEqual('function');
+  });
+
+  describe('Stack API', () => {
+    let stack = null;
+
+    beforeEach(() => {
+      stack = new Stack();
+    });
+
+    it('Should add() element to a stack', () => {
+      stack.push(5);
+      expect(stack.data).toEqual([5]);
+    });
+
+    it('Should remove() an element from the stack', () => {
+      stack.push(2);
+      stack.push(3);
+
+      expect(stack.pop()).toEqual(3);
+      expect(stack.data).toEqual([2]);
+    });
+
+    describe('peek()', () => {
+      beforeEach(() => {
+        stack.push(2);
+        stack.push(5);
+      });
+
+      it('Should return the elemet to be removed using peek()', () => {
+        expect(stack.peek()).toEqual(5);
+      });
+
+      it('Should not remove the element', () => {
+        expect(stack.peek()).toEqual(5);
+        expect(stack.pop()).toEqual(5);
+      });
+    });
+
+    it('Should maintain the FILO order of elements', () => {
+      // first in last out
+      stack.push(2);
+      stack.push(1);
+      stack.push(4);
+      stack.push(3);
+
+      expect(stack.pop()).toEqual(3);
+      expect(stack.pop()).toEqual(4);
+      expect(stack.pop()).toEqual(1);
+      expect(stack.pop()).toEqual(2);
+    });
+  });
+});

src/_DataStructures_/Stack/index.js

@@ -0,0 +1,20 @@
+class Stack {
+  constructor() {
+    this.data = [];
+  }
+
+  push(element) {
+    // add element to the last
+    this.data.push(element);
+  }
+
+  pop() {
+    return this.data.pop();
+  }
+
+  peek() {
+    return this.data[this.data.length - 1];
+  }
+}
+
+module.exports = Stack;

src/_Problems_/remove-duplicates/index.js

@@ -9,6 +9,7 @@ function removeDuplicatesUsingHashTable(str) {
     }
   }
 
+  // eslint-disable-next-line array-callback-return
   Object.keys(charHash).map((char) => {
     result += char;
   });