Added: charAt() method in string (#138)

* Create reverse.md

Added reverse method
---------

Co-authored-by: sumn2u <sumn2u@hotmail.com>

Author: Chandanmali

en/strings/charAt.md

@@ -0,0 +1,50 @@
+---
+chapter: 4
+pageNumber: 30
+---
+# charAt()
+
+str.charAt() returns the character at the given index of the string index holds the array element position.
+* using the `charAt()` method
+* using the template literal (introduced in ES6)
+
+The charAt() method takes in:
+
+Arguments: The only argument to this function is the index in the string from where the single character is to be extracted. 
+
+index: The range of this index is between 0 and length – 1. If no index is specified then the first character of the string is returned as 0 is the default index used for this function. 
+Return Value: Returns a single character located at the index specified as the argument to the function. If the index is out of range, then this function returns an empty string.
+
+```javascript
+//Example 1:
+function func() {
+	// Original string
+	let str = 'JavaScript is object oriented language';
+
+	// Finding the character at given index
+	let value = str.charAt(0);
+	let value1 = str.charAt(4);
+	console.log(value);
+	console.log(value1);
+}
+func();
+
+//Output
+j
+s
+
+//Example 2: 
+function func() {
+
+	// Original string
+	let str = 'JavaScript is object oriented language';
+
+	// Finding the character at given index
+	let value = str.charAt(9);
+	console.log(value);
+}
+func();
+
+
+//Output
+t