Promise / bluebird.js中的错误处理

Question

Whats the difference between those then calls in context of handling errors ?

.then(functionThatReturnsPromise(arg))

.then(function() {
    return functionThatReturnsPromise(arg);
})

In first example, if function functionThatReturnsPromise throws error , catch block isnt called and bluebird prints error;

Possibly unhandled Error: <msg>

Answer 1

The first one runs functionThatReturnPromise before the previous promise completes! If you write

blah()
.then( functionThatReturnsPromise(arg) )

its like writing

var firstPromise = blah();
var x = functionThatReturnsPromise(arg)
firstPromise.then(x);

Additionally, then expects to be passed a callback function but you are passing it a promise object. Its no surprise that its not working correctly.