wip: add more questions

src/data/question-groups/javascript/content/find-unique-array-values.md

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+There are serveral ways to find unique values in an array. Here are some of them:
+
+## Using `Set`
+
+```js
+const roadmaps = ['JavaScript', 'React', 'Node.js', 'Node.js', 'JavaScript'];
+const uniqueRoadmaps = [...new Set(roadmaps)];
+console.log(uniqueRoadmaps); // ['JavaScript', 'React', 'Node.js']
+```
+
+## Using `filter()`
+
+```js
+const roadmaps = ['JavaScript', 'React', 'Node.js', 'Node.js', 'JavaScript'];
+const uniqueRoadmaps = roadmaps.filter(
+  (roadmap, index) => roadmaps.indexOf(roadmap) === index
+);
+console.log(uniqueRoadmaps); // ['JavaScript', 'React', 'Node.js']
+```
+
+## Using `reduce()`
+
+```js
+const roadmaps = ['JavaScript', 'React', 'Node.js', 'Node.js', 'JavaScript'];
+const uniqueRoadmaps = roadmaps.reduce((unique, roadmap) => {
+  return unique.includes(roadmap) ? unique : [...unique, roadmap];
+}, []);
+console.log(uniqueRoadmaps); // ['JavaScript', 'React', 'Node.js']
+```
+
+## Using `forEach()`
+
+```js
+const roadmaps = ['JavaScript', 'React', 'Node.js', 'Node.js', 'JavaScript'];
+const uniqueRoadmaps = [];
+roadmaps.forEach((roadmap) => {
+  if (!uniqueRoadmaps.includes(roadmap)) {
+    uniqueRoadmaps.push(roadmap);
+  }
+});
+console.log(uniqueRoadmaps); // ['JavaScript', 'React', 'Node.js']
+```
+
+## Using `for...of`
+
+```js
+const roadmaps = ['JavaScript', 'React', 'Node.js', 'Node.js', 'JavaScript'];
+const uniqueRoadmaps = [];
+for (const roadmap of roadmaps) {
+  if (!uniqueRoadmaps.includes(roadmap)) {
+    uniqueRoadmaps.push(roadmap);
+  }
+}
+console.log(uniqueRoadmaps); // ['JavaScript', 'React', 'Node.js']
+```

src/data/question-groups/javascript/content/map.md

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+Map is another data structure in JavaScript which is similar to `Object` but the key can be of any type. It is a collection of elements where each element is stored as a Key, value pair. It is also known as a Hash table or a dictionary.
+
+The `key` can be of any type but the `value` can be of any type. The `key` is unique and immutable, whereas the `value` can be mutable or immutable.
+
+```js
+const roadmap = new Map();
+roadmap.set('name', 'JavaScript');
+roadmap.set('type', 'dynamic');
+roadmap.set('year', 1995);
+
+console.log(roadmap.get('name')); // JavaScript
+
+roadmap.delete('year');
+console.log(roadmap.has('year')); // false
+console.log(roadmap.size); // 2
+
+roadmap.clear();
+console.log(roadmap.size); // 0
+```

src/data/question-groups/javascript/content/set.md

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+Set is another data structure in JavaScript which is similar to `Array` but the values are unique. It is a collection of elements where each element is stored as a value without any keys.
+
+```js
+const roadmap = new Set();
+roadmap.add('JavaScript');
+roadmap.add('dynamic');
+roadmap.add(1995);
+
+console.log(roadmap.has('JavaScript')); // true
+
+roadmap.delete(1995);
+console.log(roadmap.has(1995)); // false
+console.log(roadmap.size); // 2
+```

src/data/question-groups/javascript/javascript.md

@@ -113,4 +113,19 @@ questions:
     topics:
       - 'OOP'
       - 'Advanced'
+  - question: What is Map in JavaScript?
+    answer: map.md
+    topics:
+      - 'Core'
+      - 'Beginner'
+  - question: What is Set in JavaScript?
+    answer: set.md
+    topics:
+      - 'Core'
+      - 'Beginner'
+  - question: How you can find unique values in an array?
+    answer: find-unique-array-values.md
+    topics:
+      - 'Core'
+      - 'Intermediate'
 ---