feat: add filter

Author: brijeshkumar-chavda

19_Iterations/7_for_each_loop.js 19_Iterations/7_for_each.js

@@ -3,9 +3,6 @@
 // What
 // - The forEach() method is a built-in function in JavaScript that allows you to iterate over the elements of an array or array-like object and perform a specified action for each element. It provides a convenient way to iterate through the elements without the need for explicit loop constructs like for or while loops.
 
-// Note
-// - The forEach() method accepts a callback function as its argument, which is invoked for each element in the array. The callback function takes three parameters: the current element being processed, the index of the current element, and the array or array-like object being iterated.
-
 // Syntax
 // array.forEach(callback(currentValue, index, array) {
 //  Perform action on each element
@@ -56,3 +53,20 @@ const array1 = [
 array1.forEach((element) => {
   console.log(element.key1);
 });
+
+// Note
+// - The forEach() method accepts a callback function as its argument, which is invoked for each element in the array. The callback function takes three parameters: the current element being processed, the index of the current element, and the array or array-like object being iterated.
+// - The forEach() method in JavaScript doesn't return a value itself. Here's a breakdown of why:
+
+// Purpose of forEach()
+// - forEach() is designed to execute a provided function once for each element in an iterable object (like arrays).
+// - Its primary focus is to perform side effects within the callback function, such as modifying elements, logging information, or triggering other actions.
+
+// Side Effects vs. Returning Values
+// - Side effects refer to actions that the callback function might perform within the loop iteration, such as changing values in the array, printing to the console, or making network requests.
+// - forEach() itself doesn't return anything after completing the loop. It simply executes the callback function for each element.
+
+// Reasons Why It Doesn't Return
+// - Focus on Iteration: The core purpose of forEach() is to iterate and potentially modify the original array or perform actions based on each element. Returning a value wouldn't align with this primary goal.
+// - Conciseness and Readability: Keeping forEach() non-returning promotes cleaner code and avoids unintended side effects related to returning values from within the loop.
+// - Functional Programming Principles: forEach() aligns with functional programming principles, where functions should ideally avoid mutable side effects and focus on pure transformations.

19_Iterations/8_filer.js

@@ -0,0 +1,47 @@
+// `.filter()`
+
+// What
+// - .filter() is a built-in method for arrays in JavaScript. It creates a new array containing only the elements that pass a test implemented by a provided function.
+// - It acts as a filtering mechanism, selecting elements from the original array based on a specific condition.
+
+// Why
+// - It offers a concise and efficient way to filter elements from an array based on a custom criteria.
+// - It avoids the need for manual looping and conditional statements within the loop, leading to cleaner code.
+
+// How
+// - You provide a callback function to .filter(). This function is called for each element in the original array.
+// - The callback function takes a single argument, which is the current element being processed in the iteration.
+// - The callback function should return a true value if the element should be included in the new filtered array, and false otherwise.
+
+// Syntax
+// const newArray = originalArray.filter(callbackFunction);
+
+// Example
+
+const array = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+// const number = array.filter((element) => {
+//   return element > 5;
+// });
+const newNumber = array.filter((element) => element > 5);
+console.log(newNumber);
+
+const books = [
+  { title: "Book One", genre: "Fiction", publish: 1981, edition: 2004 },
+  { title: "Book Two", genre: "Non-Fiction", publish: 1992, edition: 2008 },
+  { title: "Book Three", genre: "History", publish: 1999, edition: 2007 },
+  { title: "Book Four", genre: "Non-Fiction", publish: 1989, edition: 2010 },
+  { title: "Book Five", genre: "Science", publish: 2009, edition: 2014 },
+  { title: "Book Six", genre: "Fiction", publish: 1987, edition: 2010 },
+  { title: "Book Seven", genre: "History", publish: 1986, edition: 1996 },
+  { title: "Book Eight", genre: "Science", publish: 2011, edition: 2016 },
+  { title: "Book Nine", genre: "Non-Fiction", publish: 1981, edition: 1989 },
+];
+
+let userBook = books.filter((book) => book.genre === "History");
+console.log(userBook);
+
+userBook = books.filter(
+  (book) => book.edition >= 2000 && book.genre === "History"
+);
+console.log(userBook);