I have a function that calls another function over the server and returns a string back which i want to be printed in the browser's log windows, The function looks like:
function getErrorInfo() {
setTimeout(function () {
$.getJSON('Get/ErrorInfo', function (responseText) {
console.log("Log: "+responseText);
});
}, 5000);
}
getErrorInfo();
The function on the server sides does gets hits and returns a valid string But nothing is being displayed in the browser's windows Moreover the function on the server side must get hit after every 5 secs. but it only gets his on time and not again.
Please explain what am i doing wrong here.
Your basic issue is that you need to have properly formatted JSON in order to get back any result. Your result (per above) is:
3/8/2014 5:27:16 PMSystem.NullReferenceException: Object reference not set to an instance of an object. at movie.Models.Genre.GetPosts(Int32 min)
Not only is this an exception text, but it isn't valid JSON. JSON format is fully described here. Rather than calling a real service, I would recommend starting by just getting a static JSON file from the server. Then you know the data is correct.
Side Note:
The other issue here is how you print the OBJECT result from getJSON. When you try to print an object using "Console.log" it converts it to a string, which isn't probably going to show what you want. You should probably change your log statement to:
console.log(responseText);
In chrome at least, the console window will let you browse the contents of the object which can be really helpful. Between the note and the solution above I think you should have it. Best of luck!
When using $.getJSON(), the return result is required to be a valid JSON string, meaning it needs to be parsable into an object or array. In this situation, you can probably simply use $.get(), which will autodetect the return data type, or use $.ajax() and set the dataType: plain if you want to skip the JSON requirement.
On the second issue of keeping the log running, you can call getErrorInfo() from inside the setTimeout() or the callback, and it will keep running:
function getErrorInfo() {
setTimeout(function () {
$.getJSON('/echo/json/', function (responseText) {
console.log("Log: "+responseText);
getErrorInfo();
});
}, 5000);
}
getErrorInfo();
http://jsfiddle.net/Er5Lg/
In my opinion, in this situation, it is better than setInterval(), since that can get backed up and end up overriding calls, and the errors might display out of order.
Related
I need to return a value in Swift by executing JavaScript, but I am having trouble I have searched everywhere, but I can't find anything that works. To execute the JavaScript, I am using
webby.evaluateJavaScript("document.querySelector(\"pre\").innerText;")
(Webby is the name of the web view)
The JavaScript returns a string, which I would like to access in Swift. How would I accomplish this? Thanks.
To access the value you have to provide a completion handler to evaluateJavaScript, see the docs:
webby.evaluateJavaScript("<your code goes here>") { result, error in
if let result = result {
// your result handling goes here
}
}
I'm working on a Meteor project and want to get the return value of Meteor.call in template helpers on client side. At very first, I just set a variable in the call back function and get the variable's value outside the Meteor.call. I found out the code after Meteor.call doesn't execute at all. Then I searched a bit and use Session, it works. But I don't really understand the reason. Here's my original code and modified code. Can anyone explain a bit for me? Thanks!!
Original wrong code: html
<div id="text-result-main">
<h2>{{title}}</h2>
</div>
js
Template.texts.helpers({
title: function(){
var index = Router.current().params.index;
Meteor.call('getTitle', index,function(error, result){
titles = result;
});
console.log(titles);
return titles;
}});
Collection text.js
Text = new Mongo.Collection("text");
Meteor.methods({
'getTitle': function(myindex){
return Text.findOne({index: myindex}).title;
}});
The working code: js
Template.texts.helpers({
title: function(){
var index = Router.current().params.index;
Meteor.call('getTitle', index,function(error, result){
Session.set("titles",result);
});
console.log(Session.get("titles"));
return Session.get("titles");
}});
Notice that I didn't publish Collection Text to the client at all because it's just so huge. Every time when I refresh the page when running the wrong code, I can't see the content of "title" or see it on the console. But when I set the session, it works. I don't really understand how it works here. Thanks
There is two issues Asynchronicity and Reactivity
This affectation
Meteor.call('getTitle', index,function(error, result){
titles = result;
});
inside the meteor call is executed but in a asynch way. So the return of your helper is immediately called, and return a empty value.
Try it out in the console of your browser.
But then, why your template render correctly with {{title}} when you use a Session Variable ?
It's because the Session is a reactive data source, witch means that every change to it trigger a re-computation of all templates involving this piece of data.
Here is a timeline:
Methods is called
Return empty value
Method is executed, setting variable value
If the Variable is a reactive data source, template is re-computed. ( in your case, the session is a reactive data source. )
To go further
I would use a reactive var in that case, it's very close from a session variable, but the scope is limited to a template.
A good read on Reactive data source: http://richsilv.github.io/meteor/meteor-reactive-data-types/
The problem is the fact that Meteor.call() is asynchronous when paired with a callback.
So when title() starts executing, it does not wait for your Meteor.call() invocation to return a result (or possibly an error). It continues execution. This is called asynchronous execution.
In short, you are trying to log the value for the key titles which doesn't exist in Session (since the state of your asynchronous Meteor call is unknown, at this point of time).
Try moving the console log statement into the callback paired with your Meteor.call() and you can see the result once it has successfully been set in Session.
A workaround to your problem is to make your Meteor.call() synchronous like this:
Template.texts.helpers({
title: function(){
var index = Router.current().params.index;
var result = Meteor.call('getTitle', index); // <--- this is synchronous code now
Session.set("titles",result);
console.log(Session.get("titles"));
return Session.get("titles");
}});
Removing the callback makes Meteor.call() behave synchronously.
If you do not pass a callback on the server, the method invocation
will block until the method is complete. It will eventually return the
return value of the method, or it will throw an exception if the
method threw an exception.
(from http://docs.meteor.com/api/methods.html#Meteor-call)
Why not use something like this:
title: function(){
var index = Router.current().params.index;
var a = Text.findOne({index: myindex}).title;
console.log(a);
return a;
without methods
Before anyone marks it as duplicate, this post does not actually answer the question but suggests a different way altogether to solve that particular issue.
Mine is a different issue. Please let me explain.
In my case, there are various .js files (plugins) which are being loaded with jquery getscript and stored in variables. Then whenever required they will be executed (more than once)
The code for loading script (this code will only run once at the init of the system for each plugin js file)
var storedFunc;
$.getScript(pathToPluginJSFile, function( data, textStatus, jqxhr ) {
storedFunc = data;
});
All the plugins are in this format
(function(){
//lots of code here
})()
But when I checked the storedFunc variable in console, I found out that it has been stored as String variable. Like this,
"(function(){
//lots of code here
})()"
Now to execute this, I used eval, like this (this code can be executed multiple times based on the need)
eval(storedFunc)
Everything is working fine and i am happy with it, but here comes the problem, I read in somewhere that the usage of eval is kind of like a bad thing to do. So now I am afraid that thought everything is working fine, all these negativity of using eval spread on the internet might scare my client away. :(
So, please tell me how I can run that stored function (which has become a string) without using eval.
Or should I use anything else than $.getScript which does not convert a function into a string ?
Or if there is any other way altogether rewriting this plugin functionality?
Please show me the way. I am in need of this solution badly.
Any help will be appreciated.
Thanks in advance.
Understanding how $.getScript works
Seems there is some confusion on how $.getScript works. If you notice jQuery's documentation on the method, and as #Pointy made mention of in the comments, this is stated:
Load a JavaScript file from the server using a GET HTTP request, then execute it.
Here's an example: Let's pretend the contents of the file being returned is only this:
// Contents of yourExternalFile.js
console.log('Executed!');
Now, when you use $.getScript:
$.getScript(pathToPluginJSFile, function( data, textStatus, jqxhr ) {
// The script you retrieved has already executed at this point, and you will find "Executed!" in the console.
console.log('All Done');
});
Console output:
> Executed!
> All Done
The $.getScript method is not meant to be used to return a string of the content of the file. However, while that data is available in the callback, the contents of the file have already been executed. So by taking the string version of the file, and re-executing it with either new Function, or even eval, you are executing it twice on the page (jQuery does it once, and so do you).
Original Post:
Use the Function constructor instead of using eval.
// Your function as a string stored to a variable
var stringFunction = "(function(){console.log('Executed');})()";
// Use the Function constructor to create a new function:
var executableFunction = new Function(stringFunction);
// Now you can execute it
executableFunction(); // logs "Executed"
This snippet from this SO question/answer addresses the difference between eval and new Function.
eval() evaluates a string as a JavaScript expression within the current execution scope and can access local variables.
new Function() parses the JavaScript code stored in a string into a function object, which can then be called. It cannot access local variables because the code runs in a separate scope.
Additional Information (Based on comments)
Yes, you can just get the string contents of the file and store them to a variable without the contents of the file executing. You can have that function to execute anytime. You just need to use the regular get method using jquery, and set the dataType to text. This way, the script will not execute, and you can execute it as you see fit:
var storedFunction;
$.get({url: pathToPluginJSFile, dataType: 'text'})
.done(function (data) {
// Turn the script into a new function and store it
// The information in the script file has not done anything yet
storedFunction = new Function(data);
})
.fail(function () {
console.log('Failed :(');
});
The only thing you will have to watch out for, is making sure that the function was assigned to the storedFunction variable as you are making an api call, and you have to wait for that to finish before attempting to make the function execute.
// Later on, call that function anytime, and as often as you want:
storedFunction();
I'm getting this data dictionary from a db :
{"first":{"Head1":"6643Z","Head2":"1245Z"},"second":{"Head1":"1109E","Head2":"1231A"}}
and I need get only the first value for "Head1" record, for this I added a global var
in order to get the value out of the getJSON method, but run first the second alert
with a undefined value, and then run the first alert with the right value...
var message;
jQuery.getJSON("get_data.json", function(msg){
jQuery.each(msg,function (key,val){
message=val['string_data'];
return false;//trying to break
});
alert("first"+message);
});
alert("second"+message);
In order to this, how can I force have the right value on second alert, in other words,
how force to run the code in the right order....
The reason the second alert shows undefined is that when that code runs, the request hasn't completed yet.
You can make the getJSON synchronous, so that the alert doesn't run until the request is complete, but it leads to poor user experience (locks up the browser) and jQuery will be dropping support for it in an upcoming version. If you look at getJSON in the docs, you'll see it's just a wrapper that calls ajax, and if you use ajax you can specify an async: false option. (Note that this is true because you're using ajax with JSON; if it were JSON-P, you would have no synchronous option, as JSON-P is an asynchronous protocol.)
Your much better option is to embrace the asynchronous nature of web communication, and whatever you have that needs to use this data, have it supply a callback:
function getTheData(callback) {
jQuery.getJSON("get_data.json", function(msg){
var message, key;
for (key in msg) {
message = msg[key];
break; // <== SEE BELOW
}
callback(message);
});
}
getTheData(function(message) {
alert("second"+message);
});
Also note that the object you're getting back has no order, so your code getting the "first" value from it will be unreliable. You'll need to know the property key you're looking for in order to reliably get the value for that property. The order in which they appear in the text of the JSON has no effect on the order of the properties in the resulting object. (Arrays would, of course, be different.)
So for instance, if you always want the value for first, then:
function getTheData(callback) {
jQuery.getJSON("get_data.json", function(msg){
callback(msg.first);
});
}
i set up a webservice thats cross domain and needs to be contacted via json with padding
on a simple jquery codeline like this, i am successfull getting back json data.
$.getJSON("http://server/series/hist?jsonp=?", function(data){
console.log(data);
});
the webservice, will wrap the result in a function, whenever "jsonp" exists within in the url.
for those cases i used a default function name like:
myfunction({"a":1})
jquery helps me out here, and trys to call the function, that isnt existing ("myfunction()"). what i am trying to achieve instead is a simple call of the callback function (see above), to handle the data locally.
can you point me in the right direction?
thank you
I'm not quite sure what your problem actually is, but:
Interpretation 1
Assuming that by "locally" you mean "without using a callback":
That is impossible. JSON-P cannot work synchronously as it depends on the addition of a <script> element (which won't be processed until the current function has finished executing).
Interpretation 2
Assuming that by that isnt existing ("myfunction()") you mean "Your webservice always uses the function name myfunction:
Fix the webservice. jsonp=? means "Randomly generate a function name and pass it as the jsonp parameter.
The webservice must use that parameter to determine the function name used, and not use a fixed value such as myfunction.
Interpretation 3
You don't want to use JSON-P as the input, but to call your anonymous function directly.
You can't. It isn't stored anywhere you can access it. You have to rewrite your code so it isn't passed directly to getJSON:
function myFunction(data){
console.log(data);
}
$.getJSON("http://server/series/hist?jsonp=?", myfunction);
myfunction({"a":1})