Develop Reference

How to assign (add) value to a undefined item in a json object

I have a external json file and I parse it in to local object,
Currently I know I can't push value into a object so I want to assign a value to them here is my code:
//I parse my JSON into object and name it data
var data = {
...
}
// I use this object as a database so I don't list it all out
var name = "title";
var content = "hello guys";
data[name] = content;
// I wish after this script the object will have one more item like
// {
// ...
// "title": "hello guys",
// ...
//}
But the vscode's console show the following error when I run the script
TypeError: Cannot set property 'title' of undefined
If you can assign value to undefined object how can you add item in to object.
But if there is any way that can let me assign value to undefined item, I'll be very happy
Here is the full code if you need
var jsonfile = require('jsonfile')
var file = './test.json'
var data = jsonfile.readFileSync(file); //I'm very sure data isn't undefined
//console.log(data);
var name="title";
var content="hello guys";
data.post[name] = content;
jsonfile.writeFileSync(file, tmd, {spaces: 4});

currently data = undefined and you are trying to access a key in undefined that is why you are getting an error, you need to assign an empty object to data if it is undefined. you can do something like this:
var data = data || {};
var name = "title";
var content = "hello guys";
data[name] = content;

Probably data has no key named 'post'.
Try this:
data.post = data.post || {};
data.post[name] = content;
EDIT:
I know this is old, but maybe it will help someone.
Here https://nodejs.org/api/fs.html#fs_fs_readfilesync_path_options states that readFileSync returns string not data structure.

Javascript / Jquery - How to set a variable name based on a variable

This has been asked a bunch of times before but I'm not grasping it.
In the following..
var variableName = "hello";
How do I make the variable name 'variableName' based on another variable?
PHP Example
$a = 'hello';
$$a = 'hi'; // same as $hello..
echo $hello; // and $hello outputs 'hi'
I specifically need this variable variable to be used for localstorage so it may be syntax that I'm having a problem with.
What I'm Using It For (you can probbaly skip to This Seems To Work)
I want to generate a unique variable name for storing information in local storage. Variable name will be based on the post id of the wordpress post/page which I retrieve with php.
For example we will say the post id is 3333
I add the letters id to the beginning of each post id
So now I have id3333
var postIdNumber = 'id3333';
Then I get 3 other pieces of information that I want to store into local storage about this post (for simplicity I have shown an example output, not the code to get it)
var postURL = 'website.comm/a-wp-post/';
var postTitle = 'A Wordpress Post';
var postThumb = 'website.comm/images/thumb3333.jpg';
Now I want to store this information into local storage
var lsTest = { 'lsURL': postURL, 'lsTitle': postTitle, 'lsThumb': postThumb };
localStorage.setItem('lsTest', JSON.stringify(lsTest));
That works fine. Except that I want to be able to store multiple posts into local storage to retrieve later from a 'my favourite posts' page.
So I need a dynamic variable name.
For post ID 3333 I need the variable currently named lsTest to be named id3333
For post ID 4444 I need the variable currently named lsTest to be named id4444
This seems to work (Though I dont fully comprehend it)
solution modified from https://stackoverflow.com/a/5187652/3377049
var variableVariable = {}
variableVariable.postNumber = 'id3333';
var vv = 'postNumber';
jQuery('.test-div').text(variableVariable[vv]); // outputs id3333
While this does not..
var variableVariable = {} // also, should this have a ';' ?
variableVariable.postNumber = 'id3333';
var vv = 'postNumber';
var variableVariable[vv] = { 'lsURL': postURL, 'lsTitle': postTitle, 'lsThumb': postThumb };
localStorage.setItem('variableVariable[vv]', JSON.stringify(variableVariable[vv]));
In PHP I could maybe do something like this.. (for examples sake i'm mixing php variables into JS)
$uv = 'id3333';
$$uv = { 'lsURL': postURL, 'lsTitle': postTitle, 'lsThumb': postThumb };
localStorage.setItem('$$uv', JSON.stringify($$uv));

You just need to create an object of objects, keyed off of the unique post id. But then you need to stringify the object before storing it, and parse it when retrieving it.
function saveObject(key, object) {
object = JSON.stringify(object);
window.localStorage.setItem(key, object);
}
function getSavedObject(key) {
var saved = window.localStorage.getItem(key);
if (saved) {
return JSON.parse(saved);
} else {
return null;
}
}
your object:
var lsTest = {
id3333: {
postUrl: postUrl1,
postTitle: postTitle1,
postThumb: postThumb1,
},
id4444: {
postUrl: postUrl2,
postTitle: postTitle2,
postThumb: postThumb2,
}
}
store it:
saveObject('myUniqueSiteName', lsTest);
retrieve it:
var lsTest = getSavedObject('myUniqueSiteName');
adding a new post:
var lsTest = getSavedObject('myUniqueSiteName');
var postId = 'id555';
lsTest[postId] = {
postUrl: postUrl3,
postTitle: postTitle3,
postThumb: postThumb3,
}
saveObject('myUniqueSiteName', lsTest);

Variable variables are not a good idea even in PHP. Just make an array or a hash (which is an object, but it's used as a hash or map, where you can add and delete properties or entries as you please).
var posts = {};
var someId = 3333; //or '3333' if it isn't a number
posts[someId] = {
URL: postURL,
title: postTitle,
thumb: postThumb
};
localStorage.setItem('post' + someId, JSON.stringify(posts[someId]));
A property named "foo" on an object named "bar" can be accessed like so:
bar.foo = 'baz';
console.log(bar.foo);
or like so:
bar['foo'] = 'baz';
console.log(bar['foo']);
Which is the same as:
var name = 'foo';
bar[name] = 'baz';
console.log(bar[name]);
Finally, the global object in JavaScript (which in the browser is window) "holds" the global variables.
var myGlobal = 10;
console.log(window.myGlobal); // logs 10
var globalName = 'foo';
window[globalName] = 'baz';
console.log(foo); //logs 'baz'
Using global variables in general is discouraged. Using them to store posts where the name of the var is the id is highly unorthodox and many JS developers would consider it simply wrong.

Parse retrieve pointer from current user in javascript

In Parse I have the User table set up with a number of columns, most of which are Strings but one is a Pointer to another Parse Class. I want to use this pointer in a query
In Java I can access the pointer to use in my query as follows:
ParseUser currentUser = ParseUser.getCurrentUser();
ParseObject comParent = currentUser.getParseObject("ComParent");
In JavaScript I have tried using:
var currentUser = Parse.User.current();
var comParent = currentUser.get("ComParent");
But this returns undefined. What am I doing wrong?

According to the documentation:
"By default, when fetching an object, related Parse.Objects are not fetched. These objects' values cannot be retrieved until they have been fetched like so:"
var post = fetchedComment.get("parent");
post.fetch({
success: function(post) {
var title = post.get("title");
}
});
So you should write:
var currentUser = Parse.User.current();
var comParent = currentUser.get("ComParent");
comParent.fetch({
success: function(comParent) {
var name = comParent.get("Name");
alert(name); // this one will work
}
});
alert(comParent.get("Name")); // this one wont work, see below
Just remember that success is an asynchronous callback,as such comParent will not be available outside the success function as shown above, if you need to access comParent outside of success check out https://stackoverflow.com/a/27673839/1376624

Thanks. My issue was a combination of 2 things. Firstly, I was not correctly fetching the object as you rightly point out. Secondly, I was trying to fetch an object from a user which did not have an associated ComParent object (Doh!). Anyway, your solution put me onto the need to fetch the object but I don't think it is the currentUser that should have the fetch, it is comParent:
var currentUser = Parse.User.current();
var comParent = currentUser.get("ComParent");
comParent.fetch({
success: function(comParent) {
var name = comParent.get("Name");
alert(name);
}
});
Thanks again #DelightedD0D

Parse.com unable to get username from Parse.User.current?

Using javascript, after the user logs in successfully, I tried to extract the username as below:
var user = Parse.User.current();
name = user.getUsername;
The value of name is: function (){return this.get("username")}
If I use name = user.getUsername();
The value is undefined!!

user.fetch().then(function(fetchedUser){
var name = fetchedUser.getUsername();
}, function(error){
//Handle the error
});
Here the issue is Parse.User.current() method will return a user object if the user logged in or signed up successfully, but this object wont be having all the details of the user object. In order to get all the object properties you have to call fetch method on a user Object.

try
var user = Parse.User.current();
var name= user.get("username");

How to use a variable as a json atribute?

Hello im working in a generic function that sends an ajax request according with the selection made:
$('#selectAcao, #selectAno').change(function(){
var sthis = $(this);
var sthisTipo = sthis.attr('rel');
var sthisName = sthis.attr('name');
var params = {
"tipo": sthisTipo,
sthisName : sthis.children('option:selected').val(),
"atualiza" : true
}
$.atualizaSelect(params);
});
All I want is pass a "sthisName" variable as a property in "param":
var params = {
"tipo": sthisTipo,
sthisName : sthis.children('option:selected').val(),
"atualiza" : true
}
how can i do this?

That isn't JSON. JSON is a data serialisation format. What you have is a JavaScript object literal.
There is no way to define a property name using a variable at creation time for a JavaScript object.
You have to create the object first, and then add the property.
var myObject = {};
myObject[string_containing_property_name] = some_value;