Syntax : charAt(index);Example:let str=`Bangladesh is a popular country`.console.log(`The character at index 2 is ${sentence.charAt(2)} `)output: The character at index 2 is n

Syntax: replace(‘substr’,`newsubstr`);Example:Let str=’This is osman’;console.log(str.replace(‘osman’,’kader’));Result:  This is kader

Syntax: concat(str1, str2)Example:const paragraph =’JavaScript is the world's most popular programming language.’;const indexOfFirst = paragraph.indexOf(‘language'’);console.log(indexOfFirst);Result:50

Syntax: concat(str1, str2)Example:let str1=’My name is ‘;let str2=’Mohammad Osman Goni’;console.log(concat(str1,str2);Result: “My name is Mohamad Osman Goni”

Syntax: repeat(count);Example:Let str=’Bangladesh’console.log(str.repeat(3));Result: ` Bangladesh Bangladesh Bangladesh `

Syntax: split(separator)Example:let str=’ JavaScript is a text-based programming language used both on the client-side and server-side’;console.log(str.split(‘ ’);Result: Array ["JavaScript", "is", "a", "text-based", "programming", "language", "used", "both", "on", "the", "client-side", "and", "server-side"]

Syntax: trim()Example:const greeting = '   Hello world!   ';console.log(greeting);Result: `Hello world`

Syntax: toString();Example:let str = new String('Hello world');console.log(str.toString());Result: `Hello world`;

Syntax: toUpperCase()Example: let str=` JavaScript allows users to interact with web pages`console.log(str.toUpperCase());Result : "JAVASCRIPT ALLOWS USERS TO INTERACT WITH WEB PAGES"

Syntax: toLowerCase();Example: let str=’BEYOND WEBSITES AND APPS, DEVELOPERS CAN ALSO USE JAVASCRIPT TO BUILD SIMPLE WEB SERVERS AND DEVELOP THE BACK-END INFRASTRUCTURE USING NODE.JS.’console.log(str.toLowerCase())Result: "beyond websites and apps, developers can also use javascript to build simple web servers and develop the back-end infrastructure using node.js."