What's the difference between Javascript Object and JSON object
任何人都可以通过一个例子告诉我JavaScript对象和JSON对象之间的区别吗？
A Javascript object is a data type in Javascript - it makes sense only in Javascript. Often you see a Javascript object literal like this:
var obj = {
a: 1,
b: 2
};
A JSON string is a data interchange format - it is nothing more than a bunch of characters formatted a particular way (in order for different programs to communicate with each other). Because of this, it can exist inside Javascript, or in another language or simply stored inside a database or a text file.
The above Javascript object can be represented in the JSON format in Javascript like this:
var json = '{ "a": 1, "b": 2 }';
Or in C# like this:
string json = "{ "a": 1, "b": 2 }";
As you can see, a JSON is simply stored inside a string. To make it useful, the JSON string can be parsed to produce an object in any language. Because the JSON format mimics Javascript's object literal syntax, Javascript makes the parsing process easy:
var obj = eval('(' + json + ')');
Though typically you'd see:
var obj = JSON.parse(json); // for security reasons
Note that JSON is limited in that it cannot store functions - the only values it can contain are:
JSON is a text representation of a javscript object. It is effectively an object literal in javascript notation (hence the name - JavaScript Object Notation => JSON).
If you want to "compare" two object, convert the text to objects then compare keys and values.
Some examples of objects to/from text:
// Create obj using an object literal
var obj = {key: 'value'};
// Convert to text using JSON.stringify
var text = JSON.stringify(obj);
// Show the value of text
alert( text ); // {"key":"value"}
// Create a new object from text
var newObj = JSON.parse(text); // javascript object
// Show the text version of newObj
alert(JSON.stringify(newObj)); // {"key":"value"}
// Use text as code
var newObj2 = eval('(' + text + ')');
// It is indeed a string literal
alert(JSON.stringify(newObj2)); // {"key":"value"}
If you want to compare two objects, convert them from JSON to objects (if they are JSON in the first place) then do something like:
function compareObjects(a, b) {
var i, p, aProps = [], bProps = [];
// Simple test first
if (a === b) {
return true;
}
// Get properties of a
for (p in a) {
if (a.hasOwnProperty(p)) {
aProps.push(p);
}
}
// Get properties of b
for (p in b ) {
if (b.hasOwnProperty(p)) {
bProps.push(p);
}
}
// If don't have same properties, return false
if (aProps.sort().join('') != bProps.sort().join('')) {
return false;
}
// If property values aren't the same, return false
i = aProps.length;
while (i--) {
if (a[aProps[i]] !== b[bProps[i]]) {
return false;
}
}
// If passed all tests, must be equal
return true;
}
JSON stands for "JavaScript Object Notation". Basically, JSON is Javascript, but limited to just filling an object with data. By executing a JSON object, you "load" the data in memory.
JavaScript is the bigger picture, with additional lines of code to manipulate the object or to do all kinds of other stuff.
A JSON example would be this:
{
"glossary": {
"title": "example glossary",
"GlossDiv": {
"title": "S",
"GlossList": {
"GlossEntry": {
"ID": "SGML",
"SortAs": "SGML",
"GlossTerm": "Standard Generalized Markup Language",
"Acronym": "SGML",
"Abbrev": "ISO 8879:1986",
"GlossDef": {
"para": "A meta-markup language, used to create markup languages such as DocBook.",
"GlossSeeAlso": ["GML", "XML"]
},
"GlossSee": "markup"
}
}
}
}
}
A JavaScript example would be this:
var Glossary = {
"glossary": {
"title": "example glossary",
"GlossDiv": {
"title": "S",
"GlossList": {
"GlossEntry": {
"ID": "SGML",
"SortAs": "SGML",
"GlossTerm": "Standard Generalized Markup Language",
"Acronym": "SGML",
"Abbrev": "ISO 8879:1986",
"GlossDef": {
"para": "A meta-markup language, used to create markup languages such as DocBook.",
"GlossSeeAlso": ["GML", "XML"]
},
"GlossSee": "markup"
}
}
}
}
}
Notice the var Glossary = in the JavaScript?
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