如何判断Promise是否具有错误处理程序

Question

Is it possible, within a new Promise((resolve, reject) => { //here }) block to tell whether a promise has a catch handler (or error handler, more generally, as for .then(..., errorHandler) clauses)?

I'd like to print an error message in case the promise hasn't, but otherwise don't.

Answer 1

You may not be able to check in the promise scope, but you could add a listener for a un-handled rejection in the browser. A event will be emitted if there was a un-hanlded promise.

Browser

window.addEventListener('unhandledrejection', function(event) {
    // event.promise error handling 
});

Node

process.on('unhandledRejection', function(err, promise) {
    // promise error handling 
});

https://developer.mozilla.org/en-US/docs/Web/API/Window/onunhandledrejection https://thecodebarbarian.com/unhandled-promise-rejections-in-node.js.html