errorHandling.md

Error Handling

Try catch

• try: statement will keep running until error happens try裡面的程序會持續執行，直到發生了錯誤而被中斷並因此跳到catch
• catch: statement will run if and only if try has error 一但try發生錯誤，就會直接跳到catch裡面
• throw: statement throws a user-defined exception. 自製的錯誤訊息

try {
  console.log('run：會執行')
  bug()  // a error happens  
  console.log('dont run：不會執行')  // directly go to catch and it doesn't console 'dont run' 
} catch (error) {
  console.log(error)  // ReferenceError: bug is not defined 
}

// run
// ReferenceError: bug is not defined

• Error messages can be passed in multiple layers 錯誤訊息可以多層傳遞

try {
  console.log('run：會執行')
  try {
    console.log('run：會執行')
    bug();
    console.log('dont run：不會執行')
  }
  catch (innerError) {
    throw(innerError)
  }
  console.log('dont run：不會執行')
} catch (outerError){
  console.log(outerError)  // ReferenceError: bug is not defined
}

// run
// run
// ReferenceError: bug is not defined