Why can't Promise catch errors?

console.log("here we go");
new Promise( resolve => {
   setTimeout( () => {
        console.log(2)
        throw new Error("bye");//
    }, 2000);
   //    throw new Error("bye");//
}).then( value => {
    console.log( value + " world");
})
.catch( error => {
    console.log( "Error:", error.message);
});
Javascript
Apr.21,2022

first of all, in non-async functions, try-catch cannot catch exceptions generated in asynchronous operations. Promise / setTimeout are typical asynchronous operations.
secondly, catch of Promise is triggered before resolve is called throw 's Error object, or reject is called.
finally, setTimeout is an asynchronous operation, which will not be executed until the current operation is executed, so the current try-catch cannot handle the exception of setTimeout callback.

synthesize the above three points,

  1. your throw is in setTimeout , and there is no reject , Promise cannot catch to
  2. if you move to the next sentence of setTimeout , it is equivalent to your Promise without resolve before throw Error 
new Promise( (resolve, reject)=> {
setTimeout( () => {

    console.log(2)
    reject('bye');
}, 2000);
})

isn't this an error caught

Previous: Start Nexus error report: Detected execution as "root" user.

Next: Vue jumps to a non-vue page and then jumps back

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
© 2021 CodesHelper
Advertising Contact us About us
Menu