我有如下的程式碼,本來(lái)期望'core exception' 可以被'立即執(zhí)行的函數(shù)（見最後）'捕獲到，並打印出“Got it in main scope”，但沒有按預(yù)期執(zhí)行，即"Got it in main scope"沒有列印。
'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");
}
})();程式運(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
4
0
0
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();改改：
return new Promise(async (resolve, reject) => {
try {
await wrapper();
} catch(error) {
reject(new Error("core exception rises"));
}
});或：
return (async function( ) {
try {
await wrapper();
} catch(error) {
console.error(error.message);
throw new Error("core exception rises");
}
}());你程式碼的問(wèn)題是，core exception rises這個(gè)地方的Promise既沒有resolve，也沒有reject，所以你要怎麼樣？ ^^
為什麼我只有做如下的修改，才能得到預(yù)期的結(jié)果？ 是不是跟microtask有關(guān)呢？誰(shuí)能幫忙清楚解釋一下？
'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)作結(jié)果為：
wrapper exception rises
core promise rejected - core exception rises
main exception propagated
Got it in main scope
