05_Strings_methods.js

// creation of string 
let str1 = "hellow";

let str2 = 'world';
let str3 = `hellow ${str2}`;
 console.log(str3);
 console.log(str1.length);
 console.log(str1[0]);
 console.log(str1.charAt(1));
  // case cpnversion of  strings 
 let name = "   aman sharma   ";
 console.log(name.toUpperCase());
 console.log(name.toLowerCase());
 //console.log(name.trim());
 console.log(name.trimStart());
 console.log(name.trimEnd());
 // Searching methods of string 
 let sentence = "java script is easy to learn"
 console.log( sentence.indexOf("is"))
 console.log(sentence.includes("Easy"))
 console.log (sentence.startsWith("Java"))
 console.log (sentence.endsWith("learn"))
 console.log (sentence.search('easy'))

 // slicing aur extracting of the substring 
 let text = "javascript programming"
 console.log (text.slice(0,10))
 console.log(text.substring(0,9))
 console.log(text.split(" "))
 console.log(text.split(" ").join("-"))
 //replace repeat and template litral ka use 
 let msg =  " i laove java ";
 console.log ( msg.replace("java","javascript"))
 console.log("aman".repeat(3));
 let user = " Rahul";
 let age  = 21;
 let intro =` my name is ${user} and i am ${age} years old. `;
 console.log(intro);



 // ================= NAYE 3 REAL-LIFE EXAMPLES =================

// 1. Invoice/Order ID generator (padStart use karke leading zeros)
let orderId = "45";
let formattedId = "ORD-" + orderId.padStart(6, "0");
console.log(formattedId); // ORD-000045

// 2. Credit card number masking (real apps mein aisa hi dikhta hai)
let cardNumber = "1234567890123456";
let last4Digits = cardNumber.slice(-4);
let maskedCard = last4Digits.padStart(cardNumber.length, "*");
console.log(maskedCard); // ************3456

// 3. Phone number ko readable format mein dikhana (padEnd example)
let phone = "98765";
console.log(phone.padEnd(10, "0")); // 9876500000 (dummy example)

// ================= replaceAll aur concat ka use =================

// 4. Sensitive word censor karna puri sentence mein (replaceAll)
let review = "this product is bad, packaging is bad too";
let cleanReview = review.replaceAll("bad", "not good");
console.log(cleanReview);

// 5. Full name banana concat se (form data jodne jaisa real case)
let firstName = "Aman";
let lastName = "Sharma";
let fullName = firstName.concat(" ", lastName);
console.log(fullName); // Aman Sharma

// ================= at() method - real life use =================

// 6. File extension check karna (last character nikal ke)
let fileName = "resume.pdf";
console.log(fileName.at(-1)); // "f"  (last char)
console.log(fileName.slice(-3)); // "pdf" (better way for extension)

// Real use case: file type validate karna
function checkFileType(file) {
  let ext = file.slice(file.lastIndexOf(".") + 1);
  if (ext === "pdf") {
    console.log("PDF file hai, upload allowed");
  } else {
    console.log("Sirf PDF allowed hai");
  }
}
checkFileType("resume.pdf");
checkFileType("photo.jpg");