array and object confusion in json - javascript

what is the different between is
var json = [{
'id':1,
'name':'John'
}]
and
var json = {
'id':1,
'name':'John'
}
my understanding is that in code one json is an array, which means we can have multiple object which contains property of id and name. But for the second one it's an object. Is it?
and how about this one
var json = ['id':1,'name':'John']
compare to code one?

Nothing is valid JSON in your case.
The first one is an array of native javascript objects.
The second one is a javascript object.
The last one isn't valid and will throw error. It is syntactically wrong.
Use JSON.stringify() on javascript arrays or objects to make it a valid JSON.

You understanding about code one and code two are correct.
But however, the json syntax about code one and two is error. Because each json field must use double quotes, not single quotes.
so code one and code two must be written like this:
[
{
"id": 1,
"name": "John"
}
]
and
{
"id": 1,
"name": "John"
}
Now code three's syntax is error! If you want to mean an array, it must be var json = []; json['id']=1; json['name']='John'; or an object var json={'id':1,'name':John'}

JSON is a format, i.e. a way to encode Javascript objects to a sequence of characters.
Once you have a sequence of characters you can store it on disk or send it over a network and later rebuild the objects described in the sequence of characters.
You cannot encode every possible Javascript value in JSON, but only
strings
numbers (excluding NaN and infinity)
null
arrays
other objects (just the fields with values that can be encoded, not the constructor or methods)
Also, the data structure must be a tree. (You get an error if it has loops, and shared sub-trees are not detected and will be duplicated when rebuilding from JSON.)
Moreover JSON doesn't support is the presence of other fields in arrays (something that is possible in Javascript, because arrays are objects). For JSON, you have either an array or an object.
The values in your first two examples can be converted to JSON, but there are additional requirements in the format specifications. (E.g. object field names must be double quoted.)
Your last example instead is not a valid JSON string.
When you see "JSON object" or "JSON value" you must read it as "object encoded in JSON". JSON is a format, more or less like XML.

Related

Does JSON always need curly braces at the top level?

I've been learning a bit about JSON lately and was trying to understand if it always needs curly braces at the top level or if it can also be an array? Or would the array have to be wrapped in curly braces with a key name and then the array as a value?
For instance, does it have to be this:
{"title":"title 1"}
or could it be this as well:
[1,2,3]
I'm asking in the context of what the spec allows and consumers of the json file might expect, as typically from examples I've seen it, it's always curly braces with key-value pairs inside
The original specification said:
A JSON text is a serialized object or array.
… meaning that the top level needed to be either {} or [].
Many implementations ignored that restriction and allowed any JSON data type (object, array, number, string, boolean, null) to be used at the top level.
The updated specification says:
A JSON text is a serialized value. Note that certain previous
specifications of JSON constrained a JSON text to be an object or an
array. Implementations that generate only objects or arrays where a
JSON text is called for will be interoperable in the sense that all
implementations will accept these as conforming JSON texts.
So now any JSON data type is allowed at the top level, but you need to be aware that some older software might not support anything except objects and arrays at the top level.
It can be array, need not to be in curly braces
console.log(JSON.stringify([1,2,3]));
Here's more
it can be of the following:
null
boolean
number
array
object
String: only if its enclosed in quotes
Examples:
JSON.parse('{}'); // {}
JSON.parse('true'); // true
JSON.parse('"foo"'); // "foo"
JSON.parse('[1, 5, "false"]'); // [1, 5, "false"]
JSON.parse('null'); // null

Get value from json "undefined" what I have wrong?

I have this string:
[
{"id":"001",
"name":"Charlie"},
{"id":"002",
"name":"Ellie"},
]
Them, I save this string in a variable and I parse it:
function parseJSON(string){
var mylovelyJSON = JSON.stringify(string);
alert(mylovelyJSON[id]);
}
When I make my alert, I get and "undefined", I also tried with "mylovelyJSON.id", And I get the same.
Could not be a Json? I get this string from an php array.
There are many things wrong here
Your JSON is invalid
You have an extra , just before the end of the array that you need to remove
You need to parse
JSON.stringify converts a JavaScript data structure into a string of JSON.
You need to go the other way and use JSON.parse.
Square-bracket notation takes strings
mylovelyJSON[id] takes the value of id (which is undeclared so, in this case, would throw a reference error) and gets the property with the name that is the same as that value.
You need either mylovelyJSON["id"] or mylovelyJSON.id
You have an array
Your JSON consists of an array of objects, not a single object.
You need to get an object out of the array before you can access properties on it.
mylovelyJSON[0]["id"]
var json_text = '[{"id":"001","name":"Charlie"},{"id":"002","name":"Ellie"}]';
parseJSON(json_text);
function parseJSON(string){
var result_of_parsing_json = JSON.parse(string);
document.body.appendChild(
document.createTextNode(result_of_parsing_json[0]["id"])
);
}
Two things are wrong here
Your array ends with a comma, which isn't valid json
You are converting a string to javascript, and stringify does the opposite of that.
So something like this might work:
var id = 0;
function parseJSON(string){
var mylovelyJSON = JSON.parse(string);
alert(mylovelyJSON[id]);
}
Note I am assuming that id is a global variable...

Access JSON object to get Resource Bundle key/value pair

I know how to access key value pair from JSON object but in my case, the resource bundle keys are mapped to values.
e.g.
var json = {"label.name.first":"foo","label.name.second":"bar"};
Here json.label.name.first doesn't give me "foo".
Can someone help me with this?
Due to using the period character (.) in the key name, you need to use the [] notation to access its value.
console.log( json['label.name.first'] );
Additionally, you have a JavaScript object, not JSON.
The difference between a JavaScript object or JSON is that JSON is always a string. Secondly, JavaScript objects don't require the same quote standards on the key names.
If you just consider the string below, then yes it can be considred JSON (this is why if you paste it into a JSON parser, it tells you it's valid JSON):
{"label.name.first":"foo","label.name.second":"bar"}
However, if you assign that directly to a JavaScript variable then you have a JavaScript object literal, not JSON. This is because JSON is also a valid JavaScript object/array literal when it is not contained in a string:
var obj = {"label.name.first":"foo","label.name.second":"bar"};
If you were to use it as a string, then it is JSON:
var json = '{"label.name.first":"foo","label.name.second":"bar"}';
// json is a string, so it's JSON
var obj = JSON.parse(json); // parse the JSON into an object
The confusion is quote common because the JSON format is very similar to the format of JavaScript object and array literals.
Do this:
json["label.name.first"]
However, I think you are misunderstanding the . notation.
And BTW your json isn't a JSON, it is a javascript object and not its notation.
It's json["label.name.first"] that would get you "foo". Since your property's name contains characters that cannot be used in variable names.
If you're expecting to access these properties using the syntax json.label.name.first then your JSON needs to be:
var json = {
"label":{
"name":{
"first":"foo",
"second":"bar"
}
}
}
This is not right way to create object, you should create one like this.
var json={"label":{"name":{"first":"foo","second":"bar"}}};
it will also work as json string

JSON.parse on array of JSON strings not doing as expected

I'm new to javascript so learning how some of this stuff works.
I have a string that looks like: ["{\"name\":\"name\"}","{\"name\":\"Rick\"}"]
If I JSON.parse() that shouldn't it return an array of objects that have a property of name?
What I get is 2 elements in an array but they are just the JSON strings. They are not objects with property name. What am I missing?
[EDIT]
I was calling stringify() on the object and then passing it to the array instead of just passing the object as is to the array. Then I stringify() the array. I was stringifying a stringify which caused it to put the escape characters :)
If I JSON.parse() that shouldn't it return an array of objects that have a property of name?
No, it looks like the JSON defines an array with two strings in it.
This is the JSON for an array with two strings in it:
[
"{\"name\":\"name\"}",
"{\"name\":\"Rick\"}"
]
In JavaScript string literal form, that's '["{\"name\":\"name\"}","{\"name\":\"Rick\"}"]'.
This is the JSON for an array with two objects in it:
[
{
"name": "name"
},
{
"name": "Rick"
}
]
In JavaScript string literal form, that would be '[{"name":"name"},{"name":"Rick"}]'.
I guess its sholuld come as:
"[{\"name\":\"name\"},{\"name\":\"Rick\"}]"
If you lose the (escaped) quotes around the root elements you might get what you want.
E.g. something like
"[{"name":"name"},{"name":"Rick"}]"

Javascript object Vs JSON

I want to understand the basic differences clearly between Javascript object and JSON string.
Let's say I create the following JS variable:
var testObject = {one: 1,"two":2,"three":3};
Q1. Is the key/property name valid both with/without quotes? (e.g. "one" : 1)
If yes, what is the difference?
Q2: If I convert the above object using JSON.stringify(testObject), what’s the difference between the original JS object and the JSON?
I feel they are almost the same. Please elaborate on this.
Q3: For parsing a JSON string, is the method below recommended?
var javascriptObj = JSON.parse(jSonString);
Is the key/property name valid both with/without quotes ?
The only time you need to enclose a key in quotes when using Object Literal notation is where the key is a reserved word or contains a special character (if, :, - etc). It is worth noting that a key in JSON must be enclosed in double quotes.
If I convert the above object to JSON using var jSonString = JSON.stringify(testObject);, what is the difference between the 2 (JS obj and JSON)?
JSON is a data interchange format. It's a standard which describes how ordered lists and unordered maps, strings, booleans and numbers can be represented in a string. Just like XML and YAML is a way to pass structured information between languages, JSON is the same. A JavaScript object on the other hand is a physical type. Just like a PHP array, a C++ class/ struct, a JavaScript object is a type internal to JavaScript.
Here's a story. Let's imagine you've purchased some furniture from a store, and you want it delivered. However the only one left in stock is the display model, but you agree to buy it.
In the shop, the chest-of-drawers you've purchased is a living object:
var chestOfDrawers = {
color: "red",
numberOfDrawers: 4
}
However, you can't send a chest-of-drawers in the post, so you dismantle it (read, stringify it). It's now useless in terms of furniture. It is now JSON. Its in flat pack form.
{"color":"red","numberOfDrawers":4}
When you receive it, you then rebuild the chest-of-drawers (read, parse it). Its now back in object form.
The reason behind JSON, XML and YAML is to enable data to be transferred between programming languages in a format both participating languages can understand; you can't give PHP or C++ your JavaScript object directly; because each language represents an object differently under-the-hood. However, because we've stringified the object into JSON notation; i.e. a standardised way to represent data, we can transmit the JSON representation of the object to another language (C++, PHP), they can recreate the JavaScript object we had into their own object based on the JSON representation of the object.
It is important to note that JSON cannot represent functions or dates. If you attempt to stringify an object with a function member, the function will be omitted from the JSON representation. A date will be converted to a string;
JSON.stringify({
foo: new Date(),
blah: function () {
alert('hello');
}
}); // returns the string "{"foo":"2011-11-28T10:21:33.939Z"}"
For parsing a JSON string, is the method below recommended? var javascriptObj = JSON.parse(jSonString);
Yes, but older browsers don't support JSON natively (IE <8). To support these, you should include json2.js.
If you're using jQuery, you can call jQuery.parseJSON(), which will use JSON.parse() under the hood if it's supported and will otherwise fallback to a custom implementation to parse the input.
Q1: When defining object literals in javascript, the keys may include quotes or not. There is no difference except that quotes allow you to specify certain keys that would cause the interpreter to fail to parse if you tried them bare. For example, if you wanted a key that was just an exclamation point, you would need quotes:
a = { "!": 1234 } // Valid
a = { !: 1234 } // Syntax error
In most cases though, you can omit the quotes around keys on object literals.
Q2: JSON is literally a string representation. It is just a string. So, consider this:
var testObject = { hello: "world" }
var jSonString = JSON.stringify(testObject);
Since testObject is a real object, you can call properties on it and do anything else you can do with objects:
testObject.hello => "world"
On the other hand, jsonString is just a string:
jsonString.hello => undefined
Note one other difference: In JSON, all keys must be quoted. That contrasts with object literals, where the quotes can usually be omitted as per my explanation in Q1.
Q3. You can parse a JSON string by using JSON.parse, and this is generally the best way to do it (if the browser or a framework provides it). You can also just use eval since JSON is valid javascript code, but the former method is recommended for a number of reasons (eval has a lot of nasty problems associated with it).
Problems solved by JSON
Let's say you want to exchange regular JavaScript objects between two computers, and you set two rules:
The transmitted data must be a regular string.
Only attributes can be exchanged, methods are not transmitted.
Now you create two objects on the first host:
var obj1 = { one: 1,"two":2,"three":3 }; // your example
var obj2 = { one: obj1.one, two: 2, three: obj1.one + obj1.two };
How can you convert those objects into strings for transmission to the second host?
For the first object, you could send this string obtained form the literal definition '{ one: 1,"two":2,"three":3 }', but actually you can't read the literal in the script portion of the document (at least not easily). So obj1 and obj2 must actually be processed the same way.
You need to enumerate all attributes and their value, and build a string similar to the object literal.
JSON has been created as a solution to the needs just discussed: It is a set of rules to create a string equivalent to an object by listing all attributes and values (methods are ignored).
JSON normalizes the use of double-quotes for attribute names and values.
Remember that JSON is a set of rules only (a standard).
How many JSON objects are created?
Only one, it is automatically created by the JS engine.
Modern JavaScript engines found in browsers have a native object, also named JSON. This JSON object is able to:
Decode a string built using JSON standard, using JSON.parse(string). The result is a regular JS object with attributes and values found in the JSON string.
Encode attributes / values of a regular JS object using JSON.stringify(). The result is a string compliant with the JSON set of rules.
The (single) JSON object is similar to a codec, it's function is to encode and decode.
Note that:
JSON.parse() doesn't create a JSON object, it creates a regular JS object, there is no difference between an object created using an object literal and an object created by JSON.parse() from a JSON-compliant string.
There is only one JSON object, which is used for all conversions.
Going back to the questions:
Q1: The use of single of double quotes is allowed for object literals. Note that the quotes are used optionally for attributes names, and are mandatory for string values. The object literal itself is not surrounded by quotes.
Q2: Objects created from literals and using JSON.parse() are strictly the same. These two objects are equivalent after creation:
var obj1 = { one: 1, "two": 2, "three": 3 };
var obj2 = JSON.parse('{ "one": "1", "two": "2", "three": "3" }');
Q3: On modern browsers JSON.parse() is used to create a JS object from a JSON-compliant string. (jQuery has also an equivalent method that can be used for all browsers).
Q1 - in JS you only need to use quotes if the key is a reserved word or if it would otherwise be an illegal token. In JSON you MUST always use double quotes on key names.
Q2 - the jsonString is a serialised version of the input object ...
Q3 - which may be deserialised to an identical looking object using JSON.parse()
Question already has good answers posted, I am adding a small example below, which will make it more easy to understand the explanations given in previous answers.
Copy paste below snippet to your IDE for better understanding and comment the
line containing invalid_javascript_object_no_quotes object declaration to avoid compile time error.
// Valid JSON strings(Observe quotes)
valid_json = '{"key":"value"}'
valid_json_2 = '{"key 1":"value 1"}' // Observe the space(special character) in key - still valid
//Valid Javascript object
valid_javascript_object_no_quotes = {
key: "value" //No special character in key, hence it is valid without quotes for key
}
//Valid Javascript object
valid_javascript_object_quotes = {
key:"value", //No special character in key, hence it is valid without quotes for key
"key 1": "value 1" // Space (special character) present in key, therefore key must be contained in double quotes - Valid
}
console.log(typeof valid_json) // string
console.log(typeof valid_javascript_object_no_quotes) // object
console.log(typeof valid_javascript_object_quotes) // object
//Invalid Javascript object
invalid_javascript_object_no_quotes = {
key 1: "value"//Space (special character) present in key, since key is not enclosed with double quotes "Invalid Javascript Object"
}

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