Show Rails Flash messages in jquery ajax requests

In the past I struggled with having a consistent strategy for showing error messages in javascript. In rails we usually put the error/success messages in the flash, However if the request is an ajax request the flash doesn’t get used and the message shows up on the next page load.

The following code shows error/success messages using the flash properly

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#app/classes/ajax_flash.rb
#include this module in your Applicationcontroller
module AjaxFlash
extend ActiveSupport::Concern
included do
after_filter :add_flash_to_header
end
private
def add_flash_to_header
# only run this in case it's an Ajax request.
return unless request.xhr?
# add flash to header
response.headers['X-Flash'] = flash.to_h.to_json
# make sure flash does not appear on the next page
flash.discard
end
end

Include this javascript code

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(function(){
var notifiers, showErrorsInResponse, showFlashMessages;
notifiers = {
notice: 'success',
alert: 'error',
info: 'info'
};
showFlashMessages = function(jqXHR) {
var flash;
if (!jqXHR || !jqXHR.getResponseHeader) return;
flash = jqXHR.getResponseHeader('X-Flash');
flash = JSON.parse(flash);
return _.each(flash, function(message, key) {
return toastr[notifiers[key]](message);
});
};
showErrorsInResponse = function(jqXHR) {
var error, response;
if (!jqXHR || !jqXHR.responseJSON || !jqXHR.responseJSON.errors) return;
response = jqXHR.responseJSON;
error = _.map(response.errors, function(messages, property) {
return _.map(messages, function(x) {
return "" + property + " " + x;
}).join("<br />");
});
return toastr.error(error, "ERROR");
};
$(function() {
return $(document).ajaxComplete(function(event, xhr, settings) {
showFlashMessages(xhr);
showErrorsInResponse(xhr);
return xhr.responseJSON.errors;
});
});
})(this)

To use this you just need to use your normal code with respond_to

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def create
@user = User.new(params[:user])
flash[:notice] = 'User was successfully created.' if @user.save
respond_with(@user)
end

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