feat: add string object

Author: ExploitEngineer

part1 (Basics)/built-in-objects/07_math.object.js renamed to part1 (Basics)/built-in-objects/02_math.object.js

@@ -0,0 +1,45 @@
+/*
+INFO: String Object
+String is a build-in-object that allows you to work with text.
+*/
+
+/*
+A string can be created using:
+- String literal: "hello"
+- String constructor: new String("hello") (not recommended)
+*/
+let str1 = "hello";
+let str2 = new String("hello");
+
+// Properties of String
+let str = "hello";
+str.length; // 5
+
+// Methods of String
+// - Character Access
+str.charAt(index); // returns character at a position
+str.charCodeAt(index); // Unicode of character at position
+str.codePointAt(index); // Full Unicode code point (for emojis, etc.)
+
+// - Searching
+str.indexOf("h"); // finds position of first match
+str.lastIndexOf("l"); // finds position of last match
+str.includes("o"); // returns true if text if found
+str.startsWith("h"); // checks if string starts with given text
+str.endsWith("o"); // checks if string ends with given text
+
+// - Modify / Extract
+str.slice(0, 2); // extracts part of string
+str.substring(0, 2); // similar to slice but no negatives
+str.replace("a", "b"); // replaces first match
+str.replaceAll("a", "b"); // replaces all matches
+str.toUpperCase();
+str.toLowerCase();
+str.repeat(3); // repeats the string n times
+str.trim() && str.trimStart() && str.trimEnd(); // removes spaces
+
+// - Conversion
+str.split(" "); // converts string to array
+str.toString(); // returns string version
+str.valueOf(); // returns primitive value
+str.padStart(11, "*") && str.padEnd(12, "$"); // Pads string