有人可以解释一下此JavaScript / Angular代码如何工作吗？

Question

I'm reading through John Papa's angular style guide and came across this code under the Exception Handling section. Can someone please explain to me where reason comes from or how it works in that code? This is one of those JavaScript/Angular things I just don't get how it works.

/* recommended */
angular
    .module('blocks.exception')
    .factory('exception', exception);

exception.$inject = ['logger'];

function exception(logger) {
    var service = {
        catcher: catcher
    };
    return service;

    function catcher(message) {
        return function(reason) {
            logger.error(message, reason);
        };
    }
}

Answer 1

The catcher function returns a function itself that has the argument reason . In the code you posted, the function isn't called, therefore there is no reason provided, yet.

Assuming someone has injected exception somewhere else, you could call it like this:

var catcher = exception.catcher('This is a message');
var loggerError = catcher('This is the reason');

Or in a single line:

var loggerError = exception.catcher('This is a message')('This is the reason');