比如一个函数调用时缺少了一个必需的参数，这种情况应该尽早的返回异常，而不是在 Promise 中处理:
function foo(name) {
if (!name) {
return Promise.reject(new Error('name is required!'))
}
return new Promise((resolve, reject) => {/* ... */})
}Promise 只能捕获在 .then 中产生的异常，所以不应该在 Promise 外 throw new Error。
处理未捕获的异常:
function foo() {
fetch('xxx.json')
.then()
.then()
}像这个函数就是无法捕获 Promise 中产生的异常的，它会 fail silently。
然而你可以监听相关事件来处理:
// browser
window.addEventListener('unhandledrejection', event => {
// Prevent error output on the console:
event.preventDefault()
console.log('Reason: ' + event.reason)
})
window.addEventListener('rejectionhandled', event => {
console.log('REJECTIONHANDLED')
})
// node.js
process.on('unhandledRejection', reason => {
console.log('Reason: ' + reason)
})
egoist / you-dont-know-es6
《You don't know front-end》series - ECMAScript 2015
12
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