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Deleting Row by Object ID in Parse

I don't know what is wrong with my code. I am trying to delete a specific row by the object ID in Parse. Right now, it's giving me a "error" in the console. I am not sure how to fix it. Thanks!
var rowId = Parse.Object.extend("Assignment");
var queryRemove = new Parse.Query(rowId);
var obj = $(elem).parent();
queryRemove.get("$(elem).parent().attr('id')", {
success: function(obj) {
console.log(obj + " got it");
obj.destroy({
success: function() {
console.log("Deleted!");
},
error: function () {
console.log("Deleted fail!");
}
});
},
error: function(obj ,error) {
console.log("error");
}
});

From the console log it is obvious that queryRemove.get is failing as you see error handler processed.
According to Parse Api reference you should be passing a string id to query.get(), so I suppose you've mistaken in the parameter. JQuery should be evaluated and .get should receive id of an element not a string "$(elem).parent().attr('id')" which is obviously not a good id
queryRemove.get($(elem).parent().attr('id'), {
Also doesn't look like you can delete an item with .get()... Have analysed parse.com api before using it?

Retrieving a JSON.parse() string from a server

I will start by saying that I am learning how to program in jquery/javascript, and am running into an issue using JSON.parse(). I understand the format, and why people use it... but have not been able to get it to work in any of my code projects.
I have read in books/online on here in how to use it, but I think I read too much on it. I am now confused and second guessing what I know about it.
With that said, my jquery/javascript class I am taking is asking me to use it for an assignment, through AJAX using MAMP/localhost as the server.
The two codes below are for the section that I need to fill in the //TODO information. One is javascript (client-side), the other is php (server-side). I think that I've set the other //TODO information correctly, but I keep getting a token error for the JSON part.
I looked on here for a solution, but again, I think I've confused myself badly and need help. Appreciate any feedback, insight, or information.
-Javascript-
var calculateMpg = function () {
// These lines are commented out since the server will perform these checks
// if (!checkNumber("miles") || !checkNumber("gallons")) {
// return;
// }
var miles = $("#miles").val();
var gallons = $("#gallons").val();
console.log("ajax request issued.");
var result;
$.ajax({
url: "service.php?action=calculateMPG&miles="+miles+"&gallons="+gallons,
cache: false,
dataType: "text",
success: function(msg) {
console.log("ajax response received.");
// TODO: parse the JSON string returned from the server (see JSON.parse())
JSON.parse("result");
if (result.status === 'success') {
// TODO: get the mpg value returned from the server and display it to the user.
$("#mpg").val($_GET("result"));
console.log("JSON Working!");
}
else {
// TODO: get the name of the variable with the error. Hint: look at the 'fail' result from service.php
$_GET[fail(id)];
// TODO: report the error to the user using invalidNumber() function.
alert("{status: 'failure', variable: <variable name>}");
}
}
});
};
$(document).ready( function () {
$("#miles").blur(function () {
checkNumber("miles");
});
$("#gallons").blur(function() {
checkNumber("gallons");
});
$("#calculate").click(calculateMpg);
$("#miles").focus();
});
-PHP-
<?php
if ($_GET) {
if ($_GET['action'] == 'calculateMPG') {
$miles = htmlspecialchars($_GET['miles']);
$gallons = htmlspecialchars($_GET['gallons']);
// validate miles
if (strlen($miles) == 0) {
fail("miles");
}
$miles_chars = str_split($miles);
for ($i=0; $i< count($miles_chars); $i++) {
if ($miles_chars[$i] < "0" || $miles_chars[$i] > "9") {
//error_log("miles_chars check failed at: " + $i);
fail("miles");
}
}
// validate gallons
if (strlen($gallons) == 0) {
fail("gallons");
}
$gallons_chars = str_split($gallons);
for ($i=0; $i< count($gallons_chars); $i++) {
if ($gallons_chars[$i] < "0" || $gallons_chars[$i] > "9") {
fail("gallons");
}
}
// validate $miles and $gallons calling $fail along the way
$result = $miles/$gallons;
if ($result) {
success($result);
} else {
fail("mpg");
}
exit ;
}
}
function fail($variable) {
die(json_encode(array('status' => 'fail', 'variable' => $variable)));
}
function success($message) {
die(json_encode(array('status' => 'success', 'message' => $message)));
}
Edited Additional 1
I have made changes to the JSON information in regard to 'var result' (thanks to several of the responses here). I'm starting to understand JSON a bit better.
Another question I have (now) is how to isolate a part of the JSON message from the whole being transmitted?
A piece of the 'JSON.parse(msg)' returned DOES include the answer to the equation miles/gallons, but I don't know how to... extract it from the JSON.
The solution to the equation miles/gallons appears in the 'msg' output.
Thanks.
Edited Additional 2
This question has been solved! While perusing around stackoverflow for a solution to the question in my previous edited section, I found my answer here: JSON response parsing in Javascript to get key/value pair.
The answer is this: under the //TODO section asking for the mpg value, I put the following code - $("#mpg").val(result.message); - which says that in the JSON section of the variable result, take the part of the JSON marked 'message', the value being the equation solution.
Thank you to all who responded with their solutions to my problem. I appreciate the fast responses, the great suggestions, and the information in understanding JSON.
-ECP03

JSON.parse() requires that you send it a valid JSON string.
"result" is not a valid JSON string. In your success function you have defined a parameter msg - what does this contain? Try console.log(msg) at the beginning of your success function and look at the console output.

You have two options:
Option 1: -- Parse the string returned.
Change JSON.parse("result"); to:
var result = JSON.parse( msg );
Option 2: -- Request JSON instead of plain text - no need to parse
Use $.getJSON() which is shorthand for:
$.ajax({
dataType: "json",
url: url,
data: data,
success: success
});

Instead of parsing the JSON yourself, jQuery already provides you with a convenient function that will parse JSON:
var path = "service.php?action=calculateMPG&miles="+miles+"&gallons="+gallons;
$.getJSON(path, function (data) {
if (data.status == 'success') {
console.log('Success! Message:', data.message);
} else {
console.log('Failed :( Variable:', data.variable);
}
});
For your original code, what you would need to do is call JSON.parse(msg) in your success callback, which would return a JavaScript object with the values you sent from your PHP script. By specifying dataType: 'json' in the $.ajax call, jQuery does this for you. The $.getJSON method does this and some other things for you.

You need to use the result returned by the success function:
var result = JSON.parse(msg);
Then, you could do stuff like result.status.
When you put JSON.parse("result") you're saying "parse the string 'result'," which doesn't make any sense. However, if you say JSON.parse(msg) you're saying "Parse the variable that was returned from the ajax action," which makes sense.

JSON.parse() is used to convert your json data to object, then you can manipulate it easly.JSON.parse(msg); instead of JSON.parse("result").
For example:
var json = '{"value1": "img", "value2":"img2"}'
var obj = JSON.parse(json);
for ( k in obj ) {
console.log(obj[k])
}

This is totally wrong: JSON.parse("result");. .parse() expects a JSON string, e.g. the string that came back from you ajax request. You're not providing that string. you're providing the word result, which is NOT valid JSON.
JSON is essentially the right-hand side of an assignment expression.e.g.
var foo = 'bar';
^^^^^---this is json
var baz = 42;
^^---also json
var qux = ['a', 'b', 'c'];
^^^^^^^^^^^^^^^---even more json
var x = 1+2;
^^^---**NOT** json... it's an expression.
What you're doing is basically:
var x = parse;
^^^^^^---unknown/undefined variable: not JSON, it's an expression

Undefined parameter when returning data from jQuery.post to PHP

I am trying to return data from a database and populate a text field after the user enters an ID in the first text box. Currently I had the code working as long as the user did not enter a space in the ID number. Now I am attempting to allow that use case. My PHP code returns a json encoded array with three fields: first_name, last_name, and full_name.
When I use console.log(data) to view the data being returned I receive the following:
{"first_name":"Test","last_name":"Test","full_name":"Test Test"}
However in my code, I try to write data.full_name in a .val() nothing is populated, and when use the console.log I get an error saying "undefined".
Here is the whole jQuery Code:
$("#ID").blur(function () {
var params = {};
params.ID = encodeURIComponent($(this).val());
$.post("getter.php", params, function ( data ) {
if (!data) {
$("input[name=username]").val("User Not Found");
} else {
$("input[name=username]").val(data.full_name);
$("input[name=username]").attr("readonly", true);
}
});
});
Any help you can offer would be much appreciated.

Force jQuery to read the returned data as json:
$("#ID").blur(function () {
var params = {};
params.ID = encodeURIComponent($(this).val());
$.post("getter.php", params, function ( data ) {
if (!data) {
$("input[name=username]").val("User Not Found");
} else {
$("input[name=username]").val(data.full_name);
$("input[name=username]").attr("readonly", true);
}
}, "json"); // <- json forced
});
and then make sure your returned data is in proper json format (for example with json_encode in php)

Use trim() to remove spaces.
Then you can check if the parameter value is_numeric(), and if false, set a default value.

MVC: While retrieving the passed Json object from controller in view, JavaScript error

I'm passing some string messages as Json object in view.
public ActionResult SomeAction(someObject object)
{
.....
.....
if (check1)
{
return Json(new { error = Resource.someMessage1},JsonRequestBehavior.AllowGet);
}
if(check2)
{
return Json(new { error = Resource.someMessage2}, JsonRequestBehavior.AllowGet);
}
//some stuffs
return Json(new {success = "success"}, JsonRequestBehavior.AllowGet);
}
I want to retrieve the messages passed from controller and alert from My view
in view I have some javascript
function done(data) {
alert("hello");
var message = JSON.parse(data);
alert(message);
if (message["error"] != undefined) {
alert(message["error"]);
} else {
//do some stuff
}
};
what I was expecting is if passed message from controller is type error then I would get alert with the message.
The line alert("hello"); but there is no alert after that.
I get error in console
Am I doing something wrong?

If you execute the following line of code
var a = { success : "success" };
var b = JSON.parse(a);
you will get the error you have mentioned about "SyntaxError: Unexpected token o..."
Don't know why are you trying to convert your already JSON object using JSON.parse(), instead you could use this
a.success
to read the "success" value .

the variable type is detected as json object.
var x = {"error":"somemessage"};
alert(x.error)
The variable is detected as String here.
var x = JSON.parse('{"error":"somemessage"}');
alert(x.error)
If you notice, the difference is #1 starts with {(curly braces) whereas #2 starts with '(apostrophe)

Try not parsing the answer (so remove "JSON.parse(data)" line) and read everything directly from "data" variable.

You have to use data.sucess to get your result . There is no need to parse again.

Add A Table Row With Ajax Results

I have a function that takes the values returned from an ajax call and adds a row to a table that is defined in the json values, but I don't think it is fetching the table correctly. Is there anything special I need to be doing? I know the data['table_name'] variable does have the correct value in it.
Here is the code I have.
function ajaxSuccess () {
var data = JSON.parse(this.responseText);
var elementObj = document.getElementById(data['table_name']);
var i = elementObj.size() + 1;
elementObj.append('<tr><td>Date</td><td>Name</td><td>' + data['new_comment'] + '</td></tr>');
i++;
return false;
}

This is not correct.
You have js variable var elementObj = document.getElementById(data['table_name']);
And you use jquery append().
Try var elementObj = $("#"+data['table_name']); instead.
Also check console for errors, you are probably receiving this:
Uncaught TypeError: Object #<HTMLDivElement> has no method 'append'
p.s. you can also try this:
$(elementObj).append('<tr><td>Date</td><td>Name</td><td>' + data['new_comment'] + '</td></tr>');
without rewriting var elementObj to jquery variable.