Added Array methods

Author: nikhilmopidevi

_posts/2019-11-28-Commonly used JavaScript functions.markdown

@@ -25,6 +25,32 @@ Use `indexOf()` if you need the position of the passed string in the string. Use
 - [substring()][String.prototype.substring()] - This method returns the part of the string between the start and end indexes.
 - [slice()][String.prototype.slice()] - This method is quite similar to `substring()` with some [differences][StackOverflow - slice() vs substring()].
 
+## Array methods
+Following are some of the common methods from the [Array][Array] global object.
+
+- [forEach()][Array.prototype.forEach()] - This method executes a provided function once for each array element.
+- [indexOf()][Array.prototype.indexOf()] - This method returns the first index at which a given element can be found in the array, or -1 if it is not present.
+- [includes()][Array.prototype.includes()] - This method returns _true_ or _false_ based on whether the passed value is contained in the array.
+
+Just like with `String` methods, use `indexOf()` if you need the position of the value in the array. Use `includes()` if you are only concerned whether the value exists, it makes intent of the code more clear.
+
+`indexOf()` and `includes()` use [strict equality][Strict equality] (the same method used by the === or triple-equals operator) for comparing the search element with the elements of the Array. So, when used on an array containing objects, object references are compared not the actual values.
+
+Therefore, when dealing with array of objects, use `some()`, `find()`, or `findIndex()` methods.
+
+- [find()][Array.prototype.find()] - This method returns the value of the first element in the array that satisfies the provided testing function. Otherwise, `undefined` is returned.
+- [findIndex()][Array.prototype.findIndex()] - This method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1.
+- [some()][Array.prototype.some()] - This method tests whether **at least one element** in the array passes the test implemented by the provided function. It returns _true_ or _false_ appropriately.
+- [every()][Array.prototype.every()] - This method tests whether **all elements** in the array passes the test implemented by the provided function. It returns _true_ or _false_ appropriately.
+
+Following methods are used for filtering and transforming an array.
+
+- [filter()][Array.prototype.filter()] - This method creates and returns a new array with all elements that pass the test implemented by the provided function.
+- [map()][Array.prototype.map()] - This method creates and returns a new array with the results of calling a provided function on every element in the calling array.
+- [reduce()][Array.prototype.reduce()] - This method executes a provided reducer function on each element of the array, resulting in a single output value. This final output value is returned.
+- [splice()][Array.prototype.splice()] - This method modifies the contents of the array by adding or removing new elements in-place.
+- [join()][Array.prototype.join()] - This method is the opposite of [String.prototype.split()][String.prototype.split()]. It creates and returns a new string by concatenating all array elements, separating them by a specified separator string.
+
 [String]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String 
 {:target="_blank"}
 [String.prototype.indexOf()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf 
@@ -40,3 +66,32 @@ Use `indexOf()` if you need the position of the passed string in the string. Use
 [String.prototype.slice()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice 
 {:target="_blank"}
 [StackOverflow - slice() vs substring()]: https://stackoverflow.com/a/2243835/2924577
+
+[Array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
+{:target="_blank"}
+[Array.prototype.forEach()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach 
+{:target="_blank"}
+[Array.prototype.indexOf()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf 
+{:target="_blank"}
+[Array.prototype.includes()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes 
+{:target="_blank"}
+[Strict equality]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators#Identity 
+{:target="_blank"}
+[Array.prototype.find()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find 
+{:target="_blank"}
+[Array.prototype.findIndex()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex
+{:target="_blank"}
+[Array.prototype.some()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some 
+{:target="_blank"}
+[Array.prototype.every()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every 
+{:target="_blank"}
+[Array.prototype.filter()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter 
+{:target="_blank"}
+[Array.prototype.map()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map 
+{:target="_blank"}
+[Array.prototype.reduce()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce 
+{:target="_blank"}
+[Array.prototype.splice()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice 
+{:target="_blank"}
+[Array.prototype.join()]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/join 
+{:target="_blank"}