Can someone tell me what is the main difference between a JavaScript object defined by using Object Literal Notation and JSON object?
According to a JavaScript book it says this is an object defined by using Object Notation:
var anObject = {
property1 : true,
showMessage : function (msg) { alert(msg) }
};
Why isn't it a JSON object in this case? Just because it is not defined by using quotation marks?
Lets clarify first what JSON actually is. JSON is a textual, language-independent data-exchange format, much like XML, CSV or YAML.
Data can be stored in many ways, but if it should be stored in a text file and be readable by a computer, it needs to follow some structure. JSON is one of the many formats that define such a structure.
Such formats are typically language-independent, meaning they can be processed by Java, Python, JavaScript, PHP, you name it.
In contrast, JavaScript is a programming language. Of course JavaScript also provides a way to define/describe data, but the syntax is very specific to JavaScript.
As a counter example, Python has the concept of tuples, their syntax is (x, y). JavaScript doesn't have something like this.
Lets look at the syntactical differences between JSON and JavaScript object literals.
JSON has the following syntactical constraints:
Object keys must be strings (i.e. a character sequence enclosed in double quotes ").
The values can be either:
a string
a number
an (JSON) object
an array
true
false
null
Duplicate keys ({"foo":"bar","foo":"baz"}) produce undefined, implementation-specific results; the JSON specification specifically does not define their semantics
In JavaScript, object literals can have
String literals, number literals or identifier names as keys (since ES6, keys can now also be computed, which introduces yet another syntax).
The values can be any valid JavaScript expression, including function definitions and undefined.
Duplicate keys produce defined, specified results (in loose mode, the latter definition replaces the former; in strict mode, it's an error).
Knowing that, just by looking at the syntax, your example is not JSON because of two reasons:
Your keys are not strings (literals). They are identifier names.
You cannot assign a function as a value to a "JSON object" (because JSON doesn't define any syntax for functions).
But most importantly, to repeat my explanation from the beginning: You are in a JavaScript context. You define a JavaScript object. If any, a "JSON object" can only be contained in a string:
var obj = {foo: 42}; // creates a JavaScript object (this is *not* JSON)
var json = '{"foo": 452}'; // creates a string containing JSON
That is, if you're writing JavaScript source code, and not dealing with a string, you're not dealing with JSON. Maybe you received the data as JSON (e.g., via ajax or reading from a file), but once you or a library you're using has parsed it, it's not JSON anymore.
Only because object literals and JSON look similar, it does not mean that you can name them interchangeably. See also There's no such thing as a "JSON Object".
JSON has a much more limited syntax including:
Key values must be quoted
Strings must be quoted with " and not '
You have a more limited range of values (e.g. no functions allowed)
There is really no such thing as a "JSON Object".
The JSON spec is a syntax for encoding data as a string. What people call a "JSON Object" ( in javascript ) is really just an ordinary javascript object that has (probably) been de-serialized from a valid JSON string, and can be easily re-serialized as a valid JSON string. This generally means that it contains only data ( and not functions ). It also means that there are no dates, because JSON does not have a date type ( probably the most painful thing about JSON ;)
Furthermore, (side-rant...) when people talk about a "JSON Object", they almost always mean data that has the "curly-braces" at the top-level. This corresponds nicely to a javascript object. However, the JSON spec does not require that there be a single "curly-braces" object at the top-level of a JSON string. It is perfectly valid JSON to have a list at the top-level, or even to have just a single value. So, while every "JSON Object" corresponds to valid JSON, not all valid JSON strings correspond to what we would call a "JSON Object"! ( because the string could represent a list or an atomic value )
According to JSON in JavaScript,
JSON is a subset of the object
literal notation of JavaScript.
In other words, valid JSON is also valid JavaScript object literal notation but not necessarily the other way around.
In addition to reading the documentation, as #Filix King suggested, I also suggest playing around with the JSONLint online JSON validator. That's how I learned that the keys of JSON objects must be strings.
🔫 JSON: The Fat-Free Alternative to XML
JSON has been widely adopted by people who found that it made it a lot easier to produce distributed applications and services. The official Internet media type for JSON is application/json RFC 4627. JSON filenames use the extension .json.
â–º JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. JSON has been used to exchange data between applications written in any Programming language.
The JSON object is a single object that contains two functions, parse and stringify, that are used to parse and construct JSON texts.
JSON.stringify produces a String that conforms to the following JSON grammar.
JSON.parse accepts a String that conforms to the JSON grammar.
The parseJSON method will be included in the Fourth Edition of ECMAScript. In the meantime, a JavaScript implementation is available at json.org.
var objLiteral = {foo: 42}; // JavaScript Object
console.log('Object Literal : ', objLiteral ); // Object {foo: 42}foo: 42__proto__: Object
// This is a JSON String, like what you'd get back from an AJAX request.
var jsonString = '{"foo": 452}';
console.log('JOSN String : ', jsonString ); // {"foo": 452}
// This is how you deserialize that JSON String into an Object.
var serverResposnceObject = JSON.parse( jsonString );
console.log('Converting Ajax response to JavaScript Object : ', serverResposnceObject); // Object {foo: 42}foo: 42 __proto__: Object
// And this is how you serialize an Object into a JSON String.
var serverRequestJSON = JSON.stringify( objLiteral );
console.log('Reqesting server with JSON Data : ', serverRequestJSON); // '{"foo": 452}'
JSON is subset of JavaScript. Javascript was derived from the ECMAScript Programming Language Standard.
â–º ECMAScript
ECMAScript has grown to be one of the world's most widely used general purpose programming languages. It is best known as the language embedded in web browsers but has also been widely adopted for server and embedded applications. ECMAScript is based on several originating technologies, the most well-known being JavaScript (Netscape Communications)) and JScript (Microsoft Corporation).). Though before 1994, ECMA was known as "European Computer Manufacturers Association", after 1994, when the organization became global, the "trademark" "Ecma" was kept for historical reasons.
ECMAScript is the language, whereas JavaScript, JScript, and even ActionScript are called "Dialects".
Dialects have been derived from the same language. They are are quite similar to each other as they have been derived from the same language but they have undergone some changes.
A dialect is a variation in the language itself. It is derived from a single language.
SQL Language - Hibernate MySQL Dialect, Oracle Dialect,.. which have some changes or added functionality.
Information about the browser and computer of your users.
navigator.appName // "Netscape"
ECMAScript is the scripting language that forms the basis of JavaScript. JavaScript language resources.
ECMA-262 Links
Initial Edition, June 1997
PDF.
2nd Edition, August 1998
PDF.
3rd Edition, December 1999 PDF.
5th Edition, December 2009 PDF.
5.1 Edition, June 2011 HTML.
6th Edition, June 2015 HTML.
7áµ—Ê° Edition, June 2016 HTML.
8th edition, June 2017 HTML.
9th Edition, 2018 HTML.
NOTE « 4th edition of ECMAScript not published as the work was incomplete.
JSON defines a small set of formatting rules for the portable representation of structured data.
â–º Key values must be quoted, only Strings are allowed for keys. If you use other than String it will convert to String. But not recommended to use keys other than String's. Check an example like this - { 'key':'val' } over RFC 4627 - jsonformatter
var storage = {
0 : null,
1 : "Hello"
};
console.log( storage[1] ); // Hello
console.log( JSON.stringify( storage ) ); // {"0":null,"1":"Hello","2":"world!"}
var objLiteral = {'key1':'val1'};
var arr = [10, 20], arr2 = [ 'Yash', 'Sam' ];
var obj = { k: 'v' }, obj2 = { k2: 'v2' };
var fun = function keyFun() {} ;
objLiteral[ arr ] = 'ArrayVal'; objLiteral[ arr2 ] = 'OverridenArrayVal';
objLiteral[ obj ] = 'ObjectVal'; objLiteral[ obj2 ] = 'OverridenObjectVal';
objLiteral[ fun ] = 'FunctionVal';
console.log( objLiteral );
// Object {key1: "val1", 10,20: "ArrayVal", Yash,Sam: "OverridenArrayVal", [object Object]: "OverridenObjectVal", function keyFun() {}: "FunctionVal"}
console.log( JSON.stringify( objLiteral ) );
// {"key1":"val1","10,20":"ArrayVal","Yash,Sam":"OverridenArrayVal","[object Object]":"OverridenObjectVal","function keyFun() {}":"FunctionVal"}
console.log( JSON.parse( JSON.stringify( objLiteral ) ) );
// Object {key1: "val1", 10,20: "ArrayVal", Yash,Sam: "OverridenArrayVal", [object Object]: "OverridenObjectVal", function keyFun() {}: "FunctionVal"}
console.log('Accessing Array Val : ', objLiteral[ [10,20] ] );
console.log('Accessing Object Val : ', objLiteral[ '[object Object]' ] );
console.log('Accessing Function Val : ', objLiteral[ 'function keyFun() {}' ] );
â–º JSON Strings must be quoted with " and not '. A string is very much like a C or Java string. Strings should be wrapped in double quotes.
Literals are fixed values, not variables, that you literally provide in your script.
A string is a sequence of zero or more characters wrapped in quotes with backslash escapement, the same notation used in most programming languages.
🔫 - Special Symbols are allowed in String but not recomended to use.
" - Special characters can be escaped. But not recomended to escape (') Single Quotes.
In Strict mode it will throw and Error - SyntaxError: Unexpected token ' in JSON
Check with this code { "Hai\" \n Team 🔫":5, "Bye \'": 7 } over online JSON Edtions. Modes notStrict, Strinct.
var jsonString = "{'foo': 452}"; // {'foo': 452}
var jsonStr = '{"foo": 452}'; // {"foo": 452}
JSON.parse( jsonString ); // Unexpected token ' in JSON at position 1(…)
JSON.parse( jsonStr ); // Object {foo: 452}
objLiteral['key'] = 'val'; // Object {foo: 42, key: "val"}
objLiteral.key2 = 'val';
// objLiteral.key\n3 - SyntaxError: Invalid or unexpected token
objLiteral['key\n3'] = 'val'; // Object {"foo": "42", key: "val", key2: "val", "key↵3": "val"}
JSON.stringify( objLiteral ); // {"foo":"42","key":"val","key2":"val","key\n3":"val"}
Object Property accessors provide access to an object's properties by using the dot notation or the bracket notation.
â–º You have a more limited range of values (e.g. no functions allowed). A value can be a string in double quotes, number, boolean, null, object, or array. These structures can be nested.
var objLiteral = {};
objLiteral.funKey = function sayHello() {
console.log('Object Key with function as value - Its outcome message.');
};
objLiteral['Key'] = 'Val';
console.log('Object Literal Fun : ', objLiteral );
// Object Literal Fun : Object {Key: "Val"}Key: "Val"funKey: sayHello()__proto__: Object
console.log( JSON.stringify( objLiteral ) ); // {"Key":"Val"}
â–º JavaScript is the most popular implementation of the ECMAScript Standard.
The core features of Javascript are based on the ECMAScript standard, but Javascript also has other additional features that are not in the ECMA specifications/standard. Every browser has a JavaScript interpreter.
JavaScript is a dynamically typed language. That means you don't have to specify the data type of a variable when you declare it, and data types are converted automatically as needed during script execution.
Literals :
'37' - 7 // 30
'37' + 7 // "377"
+'37' + 7 // 44
+'37' // 37
'37' // "37"
parseInt('37'); // 37
parseInt('3.7'); // 3
parseFloat(3.7); // 3.7
// An alternative method of retrieving a number from a string is with the + (unary plus) operator:
+'3.7' // 3.7
Object literals RFC 7159
An object structure is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members). A name is a
string. A single colon comes after each name, separating the name from the value. A single comma separates a value from a following
name. The names within an object SHOULD be unique.
ECMAScript supports prototype-based inheritance. Every constructor has an associated prototype, and every object created by that constructor has an implicit reference to the prototype (called the object’s
prototype) associated with its constructor. Furthermore, a prototype may have a non-null implicit reference to its prototype, and so on; this is called the prototype chain.
In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior. In ECMAScript, the state and methods are carried by objects, and structure, behavior, and state are all inherited.
A prototype is an object used to implement structure, state, and behavior inheritance in ECMAScript. When a constructor creates an object, that object implicitly references the constructor’s associated prototype for the purpose of resolving property references. The constructor’s associated prototype can
be referenced by the program expression constructor.prototype, and properties added to an object’s prototype are shared, through inheritance, by all objects sharing the prototype.
As far as I understand the main difference is the flexibility.
JSON is a kind of wrapper on "JavaScript Object Notation" which forces users to obey more strict rules for defining the objects. And it does this by limiting the possible object declaration ways provided by JavaScript Object Notation feature.
As a result we have a simpler and more standardized objects which suits better on data-exchange between platforms.
So basically, the newObject in my example above is an object defined by using JavaScript Objeect Notation; but it is not a 'valid' JSON object because it does not follow the rules that JSON standards require.
This link is also quite helpful:
http://msdn.microsoft.com/en-us/library/bb299886.aspx
For the ones who still think that RFC are more important than blogs and opinion based misconceptions, let's try to answer clarifying some points.
I'm not going to repeat all the correct differences already mentioned in previous answers, here I'm just trying adding value summarizing some crucial part rfc7159
Extracts from https://www.rfc-editor.org/rfc/rfc7159
JavaScript Object Notation (JSON) is a text format for the
serialization of structured data. It is derived from the object
literals of JavaScript, as defined in the ECMAScript Programming
Language Standard, Third Edition [ECMA-262].
JSON can represent four primitive types (strings, numbers, booleans,
and null) and two structured types (objects and arrays).
An object is an unordered collection of zero or more name/value
pairs, where a name is a string and a value is a string, number,
boolean, null, object, or array.
begin-object = ws %x7B ws ; { left curly bracket
end-object = ws %x7D ws ; } right curly bracket
A JSON value MUST be an object, array, number, or string, or one of
the following three literal names: false null true
An object structure is represented as a pair of curly brackets
The names within an object SHOULD be unique.
object = begin-object [ member *( value-separator member ) ]
end-object
An object whose names are all unique is interoperable in the sense
that all software implementations receiving that object will agree on
the name-value mappings. When the names within an object are not
unique, the behavior of software that receives such an object is
unpredictable.
Examples (from page 12 of RFC)
This is a JSON object:
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": 100
},
"Animated" : false,
"IDs": [116, 943, 234, 38793]
}
}
Its Image member is an object whose Thumbnail member is an object and
whose IDs member is an array of numbers.
There is really no such thing as a "JSON Object".
Really?
First you should know what JSON is:
It is language agnostic data-interchange format.
The syntax of JSON was inspired by the JavaScript Object Literal notation, but there are differences between them.
For example, in JSON all keys must be quoted, while in object literals this is not necessary:
// JSON:
{ "foo": "bar" }
// Object literal:
var o = { foo: "bar" };
The quotes are mandatory on JSON because in JavaScript (more exactly in ECMAScript 3rd. Edition), the usage of reserved words as property names is disallowed, for example:
var o = { if: "foo" }; // SyntaxError in ES3
While, using a string literal as a property name (quoting the property name) gives no problems:
var o = { "if": "foo" };
So for "compatibility" (and easy eval'ing maybe?) the quotes are mandatory.
The data types in JSON are also restricted to the following values:
string
number
object
array
A literal as:
true
false
null
The grammar of Strings changes. They have to be delimited by double quotes, while in JavaScript, you can use single or double quotes interchangeably.
// Invalid JSON:
{ "foo": 'bar' }
The accepted JSON grammar of Numbers also changes, in JavaScript you can use Hexadecimal Literals, for example 0xFF, or (the infamous) Octal Literals e.g. 010. In JSON you can use only Decimal Literals.
// Invalid JSON:
{ "foo": 0xFF }
Here is one surprising difference: you can not use undefined in json and all object fields with undefined values will disappear after JSON.stringify
let object = { "a": undefined } ;
let badJSON= '{ "a": undefined }';
console.log('valid JS object :', object );
console.log('JSON from object:', JSON.stringify(object) );
console.log('invalid json :', JSON.parse(badJSON) );
🙈🙉🙊
Javascript Object Literal vs JSON:
Object literal syntax is a very convenient way to create javascript objects
The JSON language, which stands for 'Javascript object notation', has its syntax derived from javascript object literal syntax. It is used as a programming language independent textual data transfer format.
Example:
JS object notation, used in JS to create objects in the code conveniently:
const JS_Object = {
1: 2, // the key here is the number 1, the value is the number 2
a: 'b', // the key is the string a, the value is the string b
func: function () { console.log('hi') }
// the key is func, the value is the function
}
Example of JSON:
{"widget": {
"debug": "on",
"window": {
"title": "Sample Konfabulator Widget",
"name": "main_window",
"width": 500,
"height": 500
},
"image": {
"src": "Images/Sun.png",
"name": "sun1",
"hOffset": 250,
"vOffset": 250,
"alignment": "center"
},
"text": {
"data": "Click Here",
"size": 36,
"style": "bold",
"name": "text1",
"hOffset": 250,
"vOffset": 100,
"alignment": "center",
"onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
}
}}
Main differences:
All object keys in JSON must be strings. In Javascript object keys can be strings or numbers
All strings in JSON must be quoted in "double quotes". Whereas in Javascript both single quotes and double quotes are allowed. Even with no quotes in the Javascript object notation the object keys are implicitly casted to strings.
In JSON a function cannot be defined as a value of an object (since this is Javascript specific). In Javascript this is completely legal.
Javascript build in JSON object:
JSON objects can be easily converted to Javascript and vice versa using the built in JSON object which Javascript offers in its runtime. For example:
const Object = {
property1: true,
property2: false,
}; // creating object with JS object literal syntax
const JSON_object = JSON.stringify(Object); // stringify JS object to a JSON string
console.log(JSON_object); // note that the (string) keys are in double quotes
const JS_object = JSON.parse(JSON_object); // parse JSON string to JS object
console.log(JS_object.property1, JS_object.property2);
// accessing keys of the newly created object
Related
What types, and what serialisation pattern, can I use to ensure I have arbitrary-precision numbers in my JavaScript program while it's running, but the state is serialised to / deserialised from JSON with a minimum of pain?
I am writing an application that makes heavy use of numbers with higher precision than allowed by the ECMAScript native Number type. So I need to use a custom type (currently BigNumber) to represent those values.
I am looking hungrily at the proposed BigInt type, which when implemented as standard will be an improvement for many applications including the one I'm writing. However that won't help at all with JSON, which knows nothing about BigInt any more than BigNumber.
Whichever custom type I choose, there are many values of this type throughout the application state. So much that it's worth considering a custom hook in the serialisation / deserialisation layer that will handle transforming it to / from JSON.
Presumably the JSON document will have to represent the values as JSON native types (e.g. Object or String instances). How then, when de-serialising the entire complex application state, to reliably recognise and de-serialise those instances among all the others, to the correct value of the correct BigInt or BigNumber type?
How can I serialise that state, such that any BigNumber (or insert some other arbitrary-precision number type) value reliably survives the serialisation / de-serialisation process, to correct values of the correct type?
If modifying the type (by adding a property to the prototype) is feasible, there is a toJSON hook from JSON.stringify, designed specifically to help custom types collaborate with JSON serialisation.
If an object being stringified has a property named toJSON whose value is a function, then the toJSON() method customizes JSON stringification behavior: instead of the object being serialized, the value returned by the toJSON() method when called will be serialized.
So you could add a new method to the BigNumber class:
BigNumber.prototype.toJSON = function toJSON(key) {
return {
_type: 'BigNumber',
_data: Object.assign({}, this),
};
};
state = {
lorem: true,
ipsum: "Consecteur non dibale",
dolor: new BigNumber(107.58),
sit: { spam: 5, eggs: 6, beans: 7 },
amet: false,
};
serialisedState = JSON.stringify(state);
console.debug("serialisedState:", serialisedState);
// → '{"lorem":true,"ipsum":"Consecteur non dibale","dolor":{"_type":"BigNumber","_data":{"s":1,"e":2,"c":[1,0,7,5,8]}},"sit":{"spam":5,"eggs":6,"beans":7},"amet":false}'
You can then recognise those specific objects when de-serialising, using the reviver parameter of JSON.parse:
If a reviver is specified, the value computed by parsing is transformed before being returned. Specifically, the computed value and all its properties (beginning with the most nested properties and proceeding to the original value itself) are individually run through the reviver. Then it is called, with the object containing the property being processed as this, and with the property name as a string, and the property value as arguments. [If the return value is not undefined], the property is redefined to be the return value.
function reviveFromJSON(key, value) {
let result = value;
if (
(typeof value === 'object' && value !== null)
&& (value.hasOwnProperty('_type'))) {
switch (value._type) {
case 'BigNumber':
result = Object.assign(new BigNumber(0), value._data);
}
}
return result;
}
state = JSON.parse(serialisedState, reviveFromJSON);
console.debug("state:", state);
// → { … dolor: BigNumber { s: 1, e: 2, c: [ 1, 0, 7, 5, 8 ] }, … }
One potential solution is the Granola library for Node.js.
granola provides a JSON compatible stringifier and parser with support for modern language and object primitives.
This would require:
Convert the application from using BigNumber values to BigInt values.
Wait for tools to support BigInt in the entire build tool chain.
The question speaks for itself. JSON isn't a type. You have the function JSON.stringify(object). My opinion is that the resulting String from this function is JSON, not the object which is stringified. And if that is true JSON would be a String ?
JSON (JavaScript Object Notation) is a way to format object data as a string. You are correct in saying JSON is not a type. JSON.stringify(object) takes an object and returns a string. The string will contain the data of the object, but in a human-readable form.
So JSON is the string of an object.
JSON(JavaScript Object Notation) is a file-format that uses human-readable text.
In the following snippet, you can see that I created a JavaScript object (object) then I used JSON.stringify(object) to get the JSON version (string). typeof is used to show you the type of the element next to it.
typeof object will give you the type of object
You can also notice that there are some changes. For example, properties names are wrapped with double quotes " ", the values are wrapped with double quotes instead of simple,...
const object = {
propertyA : "This is my value A",
propertyB : [1,2,3],
propertyC : {test: 'Nice'}
};
console.log(typeof object);
console.log(JSON.stringify(object));
console.log(typeof JSON.stringify(object));
JSON is a Objects Notation (serialised), but JSON has specifice characteristics that it can be converted into/from specific syntax of String (for usage into different languages/platforms or for data transfer into different systems).
In javaScript :
to convert syntactically_correct_string to JSON we use JSON.parse(inputStringHere),
and to convert a JSON into String we use JSON.stringify(inputJSONobject).
Is it possible to perform complex queries over a JSON object? I am open to JavaScript or jQuery solutions, the easier the better. I'm envisioning some kind of functional programming language similar to LINQ or SQL.
I Prefer no other third party libraries or add-ons.
UPDATE
From the looks of early answers, an add-on is going to be necessary. In that case, I prefer an add-on that requires no installation process. Something that deploys with the software publish (like jQuery) is fine (e.g. sets of *.js files).
Check out: Is there a query language for JSON?
From that thread:
JaQL(Wiki)
JsonPath.
Json Query
By the time you're interacting with it, it's not a "JSON object," it's a JavaScript object. ("JSON objects" only exist in terms of the data notation.) JavaScript itself doesn't have any advanced functional programming constructs, so you'd need third party libraries for that sort of thing. JavaScript pretty much just has property accessors, an operator for "does this object have a property with this name?" (in, hasOwnProperty), and as of the 5th edition (not yet widely supported), some handy array-specific features like forEach, every, map, filter, and the like.
Use JSON.stringify and a replacer callback to achieve this:
function replacer(match, offset, fullstring)
{
return replacer.str;
}
replacer.str = "\u0022filterValues\u0022:[\u0022hi\u0022,\u0022bye\u0022]"; /* Use DOM node value */
var foo = JSON.stringify({
"Region": {
"filterField": "kw_Region",
"filterValues": [
"aa",
"bb"
]
},
"ApplicationName": {
"filterField": "kw_ApplicationName",
"filterValues": [
"aa",
"bb"
]
},
"IssueType": {
"filterField": "kw_IssueType",
"filterValues": [
"aa",
"bb"
]
},
"Outage": {
"filterField": "kw_Outage",
"filterValues": [
"aa",
"bb"
]
},
"Priority": {
"filterField": "kw_Priority",
"filterValues": [
"aa",
"bb"
]
}
}).replace(/"filterValues[^\]]+./g, replacer)
Here is some documentation on the two JSON methods for serialization and transformation, stringify and parse:
JSON.parse(source, reviver)
This method parses a JSON text to produce an object or array. It can throw a SyntaxError exception.
The optional reviver parameter is a function that can filter and transform the results. It receives each of the keys and values, and its return value is used instead of the original value. If it returns what it received, then the structure is not modified. If it returns undefined then the member is deleted.
The reviver is ultimately called with the empty string and the topmost value to permit transformation of the topmost value. Be certain to handle this case properly, usually by returning the provided value, or JSON.parse will return undefined.
if (k === "") return v
JSON.stringify(value, replacer, space)
The stringify method produces a JSON text from a JavaScript value. If value is an object or array, the structure will be visited recursively to determine the serialization of each membr or element. The structure must not be cyclical.
When an object value is found, if the object contains a toJSON method, its toJSON method will be called and the result will be stringified. A toJSON method does not serialize: it returns the value represented by the name/value pair that should be serialized, or undefined if nothing should be serialized. The toJSON method will be passed the key associated with the value, and this will be bound to the object holding the key.
You can provide an optional replacer method. It will be passed the key and value of each member, with this bound to the containing object. The value that is returned from your method will be serialized. If your method returns undefined, then the member will be excluded from the serialization.
If the replacer parameter is an array, then it will be used to select the members to be serialized. It filters the results such that only members with keys listed in the replacer array are stringified.
Values that do not have JSON representations, such as undefined or functions, will not be serialized. Such values in objects will be dropped; in arrays they will be replaced with null. You can use a replacer function to replace those with JSON values. JSON.stringify(undefined) returns undefined.
The optional space parameter produces a stringification of the value that is filled with line breaks and indentation to make it easier to read.
If the space parameter is a non-empty string, then that string will be used for indentation. If the space parameter is a number, then the indentation will be that many spaces.
var alias = {"Clark":"","phone":""};
function kryptonite(key)
{
var replacement = {};
for(var cursor in this)
{
if(cursor in alias)
replacement[cursor] = this[cursor]
}
return replacement;
}
var contact = {
"Clark":"Kent",
"Kal El":"Superman",
"phone":"555-7777"
}
contact.toJSON = kryptonite;
var foo = JSON.stringify(contact) // "{"Clark":"Kent","phone":"555-7777"}"
References
ECMAScript Wiki:JSON Support
MDN:JSON.parse Examples
MDN:JSON.stringify toJSON behavior
MSDN:toJSON Method
Opera:JSON.parse
hmm... YQL does this sort of thing, but that would be a third party.
you could filter an array with the jQuery $.grep(array,filterfn) method
var newArr = $.grep(oldArr,function(elInArray,index){
return elInArray.key === somevalue;
});
and you can of course use a regexp in there if you wish, or use more complex conditions, such as checking multiple keys, keys within keys, arrays within keys, etc.
I always had this silly doubt in mind but never had come up with the solution.
I have seen several kind of arrays but I don't know the difference between them. I don't know how to explain exactly but it's most when passing parameters with jQuery.
See:
{ 'choices[]': ["Jon", "Susan"] } in $("#objectID").load("test.php", { 'choices[]': ["Jon", "Susan"] } );
What's the {}? (does this mean it's an array?). Why is choices[] quoted? I have already seen unquoted ones, what's the difference? I presume that choices is the associative name and ["Jon", "Susan"] is the value, is it right?
The braces { } will construct an object using the object literal notation. You are not constructing an array, but an object, even though JavaScript objects can also be thought of as associative arrays.
Further reading:
Douglas Crockford: A Survey of the JavaScript Programming Language (scroll to the Objects section)
Apart from the few primitive types (numbers, strings, booleans, null and undefined) everything is an object in JavaScript (even functions).
Objects are basically containers of properties, which happen to be very useful for collecting and organizing data.
The object literal notation (the braces { } method that you describe) is very handy for creating objects:
var myFirstObject = {
'name': 'Bobby',
'surname': 'Smith'
};
The quotes around property names are optional if the name would be a legal JavaScript identifier and not a reserved word. That is why 'choices[]' is quoted in your example, because it is not a legal JavaScript identifier. A property's name can be any string as long as it is quoted.
Objects can also contain other objects, so they can easily represent trees or graphs:
var myFlight = {
'airline': 'Airline Name',
'number': 'AN700',
'departure': {
'IATA': 'SYD',
'time': '2010-09-04 23:10:00'
},
'arrival': {
'IATA': 'LAX',
'time': '2010-09-05 05:14:00'
}
};
JavaScript objects also happen to be a convenient hash table data structure, and can be used as associative arrays as mentioned earlier. You could easily do the following:
var myHashTable = {};
myHashTable['name'] = 'Bobby';
myHashTable['surname'] = 'Smith';
// subscript notation:
alert(myHashTable['name'] + ' ' + myHashTable['surname']);
// dot notation: (equivalent)
alert(myHashTable.name + ' ' + myHashTable.surname);
{} are for javascript objects aka JSON notation. [] are for arrays.
{attributeName1: 'attributeValue1', attributeName2: 'attributeValue2'}
vs
['arrayValue1', 'arrayValue2']
{} is the syntax for creating an object. [] is the syntax for creating an array. Objects are collections of items in the format key->value; arrays are collections of items with the value stored only.
'choices[]' is quoted because choices[] (without the quotes) would have a special meaning in Javascript. By quoting it, it is treated as a string and is therefore allowed to be the key in the object. You only need to quote object keys where they would otherwise have a special meaning in Javascript.
JavaScript has arrays and objects (which can be considered associative arrays). An object looks like this:
var someObject = {
'key': 'value',
'anotherKey': 'anotherValue'
};
And an array looks like this:
var someArray = [
'value',
'anotherValue'
];
An array is technically a subClass of Object whose keys are zero-indexed numbers though creating on object with numbers as keys will not give you an array. (Its also a syntax error because keys must be strings)
{1: 'foo'} != ['foo']
{'1': 'foo'} != ['foo']
I am a newbie to JSON & hence I am not sure what $.toJSON(params) means.
Please explain what this does.
It could be this jQuery plugin
var myObj = {};
myObj.propA = "a";
myObj.propB = "b";
myObj.propC = "c";
var jsonString = $.toJSON(myObj); // same as jQuery.toJSON(myObj)
// output: '{ "propA" : "a", "propB" : "b", "propC" : "c" }'
See: http://www.json.org/js.html
A JSON stringifier goes in the opposite direction, converting JavaScript data structures into JSON text. JSON does not support cyclic data structures, so be careful to not give cyclical structures to the JSON stringifier.
var myJSONText = JSON.stringify(myObject, replacer);
If the stringify method sees an object that contains a toJSON method, it calls that method, and stringifies the value returned. This allows an object to determine its own JSON representation.
The stringifier method can take an optional array of strings. These strings are used to select the properties that will be included in the JSON text.
The stringifier method can take an optional replacer function. It will be called after the toJSON method (if there is one) on each of the values in the structure. It will be passed each key and value as parameters, and this will be bound to object holding the key. The value returned will be stringified.
So if you have a $.toJSON() method, it could be a badly implemented function to "stringify", or it could be a method that returns the "JSON Representation" of $
It passes the variable params as an argument to the method named toJSON attached to the object stored in the (unhelpfully named) variable $.
Based on the name, it probably converts the contents of the params variable to a String formatted according to the JSON specification.