Try-catch

1. try, catch
2. promise
3. async, await

• try catch - yozgan kodimizda qandaydir xato bo'lsa anashu xatolikni tutib oladigan block, agar kodimizda xatolik bo'lsa projectni to'xtatib qo'yadi, try-catch orqali shu chiqqan xatoni userga custom xolatda ko'rinadigan qilsak bo'ladi.

Syntax of try catch

try{
  console.log('try block') 
}catch(error){
  console.log('error has occured', error.stack) 
} finally{
  console.log('this always runs') 
}

1-console try blockddagi kodda xatolik bo'lmasa ishlaydi

2-console try blockdagi kodda xatolik bo'lsa shu xatolikni catch bilan tutib olib uni consolega chiqaramiz.

3-console try yoki catch blok ishga tushganda chiqadi, ya'ni har doim.

Error methods

1. error.name - errorni qanaqa turdaligini bildiradi, // ReferenceError
2. error.message - qanday errorligini bildiradi, // is not defined
3. error.stack - errorni umumiy ko'rinishi, // ReferenceError: * is not defined

Example

try{
  console.log(a) 
}catch(error){
  console.log('error has occured', error.stack) 
} finally{
  console.log('this always runs') 
}   // a e'lon qilinmaganligi uchun xatolik chiqadi, catch dagi ma'lumotlar

Throw

• throw-orqali catch qismiga xatoliklarni userga custom xolatda jo'natsak bo'ladi.

let data = `{"age":30}`;
try {
  let user = JSON.parse(data);
    if (!user.name) {    
    throw new SyntaxError("Incomplete data: no name");  
    }  
    console.log(user.name);
} catch (error) {
  console.log("JSON error:", error.name);
} // data ni ichida name yoqligi uchun xato chiqadi va throw orqali 
// xatoni ozimizga custom xolatda chiqaryapmiz

Error types

1. ReferenceError
2. SyntaxError
3. TypeError

//ReferenceError
let x = 5;
try {
  x = y + 1;
} catch (error) {
   console.log(error instanceof ReferenceError);
   console.log(error.name);
   console.log(error.message);
}

//SyntaxError
let a=5;
let a=10; // a already declared
==============
try {
  eval("console.log('hello)"); 
} catch (error) {
  console.log(error instanceof SyntaxError);\ 
  console.log(error.name);  
  console.log(error.message);
}   // invalid or unexpected token (')

//Typeerror
const a=5;
a=7;  // const is not changeable
==========
let num = 5;
try {
  console.log(num.toUppercase());
} catch (error) {
  console.log(error.name);
} // number has not toUpperCase method

//RangeError
let num = 5;
try {
  console.log(num.toPrecision(500));
} catch (error) {
  console.log(error.name);
  console.log(error.message)
} 

Promise

• promise - asinxron amallarni bajarish uchun ishlatiladi, ya'ni qanday amalni kutib turadi va keyin natijani yoki xatolikni chiqaradi.
• promise o'ziga 2 ta parametr oladi (resovle va reject), resovle- hich qanday muammo bo'lmaganda ishlaydi, reject esa kodda qandaydir muammo bo'lsa ishlaydi.

//Syntax
new Promise((resolve, reject)=>{
 let error = false;
 if(!error){
   resovle()
 } else{
   reject()
 }
})

//Example
let promise = new Promise((resolve, reject) => {
  let num = 3; 
  if (num == 3) {
      resolve("Test passed");
  } else {    
      reject("Test didn't pass");
  }
});
promise
  .then((message) => {
    console.log("This is in the then block", message);
   })  
  .catch((message) => {
    console.log("This is in the catch block", message);
});

async, await - xatolik bo'lsa try catch bilan tutib olishimiz mumkin bo'ladi

//Syntax
async function getData(){
  try{
    await render();
  } catch(error){
    console.log(error.message)
  }
}