函数返回undefined而不是Boolean

Question

I have a function that checks if the provided link is reachable, and it returns a Boolean value.

$scope.isReachable = function(uri) {
    var url = 'http://example.com/file.pdf';

    $http({
      method: 'GET',
      url: url
     })
     .success(function(data, status, headers, config) {
      console.log("I See it");
      return true;
    })
     .error(function(data, status, headers, config) {
      console.log("I don't");
      return false;
     });
  };

I have done a lot of functions and the return statements are fine, but this one. I don't know why but it seems very odd to me. I'm not quite sure if it's the $http function, but it shouldn't matter, right? I can see the console messages but the boolean value.

Answer 1

Those return statements are returning inside the functions they belong to, which are the anonymous functions passed to success and error .

The isReachable function does NOT return any value. What it does is simply perform the request and pass it two callbacks.

I don't have context of the rest of the code, but this is async programming and you are doing a request and passing callbacks. The best way to go here in my opinion is passing the callbacks to the isReachable function like this:

var isReachableCallback = function(data, status, headers, config) {
  console.log("I See it");
  return true;
};

var isNotReachableCallback = function(data, status, headers, config) {
  console.log("I don't");
  return false;
};

$scope.isReachable = function(uri, isReachableCallback, isNotReachableCallback) {
    var url = 'http://example.com/file.pdf';

   return $http({
      method: 'GET',
      url: url
     })
     .success(isReachableCallback)
     .error(isNotReachableCallback);
  };

Not sure if these are best practices in Angular world though, I'm just trying to illustrate what's going on with the example.