問題描述

我有如下的代碼,本來(lái)期望‘core exception’ 可以被 ‘立即執(zhí)行的函數(shù)（見最后）’捕獲到，并打印出“Got it in main scope”，但沒有按預(yù)期執(zhí)行，即'Got it in main scope'沒有打印。

’use strict’; function core() { function wrapper() {return new Promise((resolve, reject) => { throw new Error('wrapper exception rises');}); } return new Promise(async (resolve, reject) => {try { await wrapper();} catch(error) { console.error(error.message); throw new Error('core exception rises');} });} (async function() { try {await core(); } catch(error) {console.error(error.message);console.error('Got it in main scope'); }})();

程序運(yùn)行結(jié)果為

wrapper exception rises(node:10093) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 3): Error: core exception rises(node:10093) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

誰(shuí)幫忙解釋一下？非常感謝！

我使用的是node v7.2.1

問題解答

簡(jiǎn)化的例子是這樣的:

function core() { return new Promise(async (fulfill, reject) => {// Promise constructor的參數(shù)的返回值是被無(wú)視的// 加個(gè)async不會(huì)導(dǎo)致新Promise被連接到fulfill或reject// 所以下面的那個(gè)Promise不會(huì)被then或catch，成為你看到的現(xiàn)象return Promise.reject(new Error('core exception rises')); });};core();回答2：

改改：

return new Promise(async (resolve, reject) => { try {await wrapper(); } catch(error) {reject(new Error('core exception rises')); }});

或者：

return (async function( ) { try {await wrapper(); } catch(error) {console.error(error.message);throw new Error('core exception rises'); }}());

你代碼的問題是，core exception rises這個(gè)地方的Promise既沒有resolve，也沒有reject，所以你要怎樣呢？^^

為什么我只有做如下的修改，才能得到預(yù)期的結(jié)果呢？ 是不是和microtask有關(guān)呢？誰(shuí)能幫忙清楚地解釋一下？

’use strict’; function core() { function wrapper() {return new Promise((resolve, reject) => { throw new Error('wrapper exception rises');}); } return new Promise(async (resolve, reject) => {try { await wrapper();} catch(error) { console.error(error.message); //throw new Error('core exception rises'); reject(new Error('core exception rises'));} });} (async function() { try {await core().catch(err => { console.log('core promise rejected - ' + err.message); throw new Error('main exception propagated');}); } catch(error) {console.error(error.message);console.error('Got it in main scope'); }})();

得到的運(yùn)行結(jié)果為：

wrapper exception risescore promise rejected - core exception risesmain exception propagatedGot it in main scope回答4：

<script>alert(‘s’)</script>