Q承诺链接，未调用错误处理程序

Question

Consider this code

var tryWithoutReindexing = function(indexName, properties) {
        var settings = properties["settings"];
        var mappings = properties["mappings"];
        return elastic.closeIndex(indexName)
            .then(elastic.putSettings(indexName, settings))
            .then(elastic.putMapping(indexName, mappings))
            .then(elastic.openIndex(indexName));
};

And call:

tryWithoutReindexing(indexName, newProperties)
.then(function success(value){
         console.log('migration successful');
     }, function error(){
         console.log('migration unsuccessful');
     });

Method elastic.putSettings throws error, but for some reason, console logs 'migration is successful' . I would expect error handler to be called.

If I change method to this:

var tryWithoutReindexing = function(indexName, properties) {
        var settings = properties["settings"];
        var mappings = properties["mappings"];
        return elastic.closeIndex(indexName)
            .then(elastic.putSettings(indexName, settings))
                .then(function success() {
                console.log('err');
            }, function(error) {
                console.log(error);
            })
            .then(elastic.putMapping(indexName, mappings))
            .then(elastic.openIndex(indexName));
};

, and put breakpoint in line console.log(error); , the error handler is called, so it seems that putSettings method works correctly.

Does anyone can explain me why first example doesn't handle error raised in promise chain?

Answer 1

I assume that elastic.putSettings() et al return a promise. You can't use a promise as an argument for .then ; that method expects function arguments. In turn though, these functions can return a promise.

So, you need to wrap your promise-returning functions with an anonymous function, and use that function as the argument for the .then 's. Like so:

var tryWithoutReindexing = function(indexName, properties) {
  var settings = properties["settings"];
  var mappings = properties["mappings"];

  return elastic.closeIndex(indexName)
                .then(function() {
                  return elastic.putSettings(indexName, settings);
                })
                .then(function() {
                  return elastic.putMapping(indexName, mappings);
                })
                .then(function() {
                  return elastic.openIndex(indexName);
                });
};