How come this:
data-something='{property:1}'
doesnt work, but this
data-something='{"property":1}'
does. Does it
Because JSON requires that object keys be quoted. This is mandated by the JSON specification; accepting non-quoted keys would mean that the implementation is not JSON-compliant.
This decision was made to side-step the issue of reserved keywords in JavaScript. It was desired that valid JSON also be a valid JavaScript expression, and to make that happen you would have to quote keys like return and function. To simplify specification of the JSON language, it was decided to require that all keys be quoted rather than maintain a list of keys that must be quoted and thereby complicate the JSON grammar (as well as tie the JSON language more closely to the JavaScript language than would otherwise be required).
Related
I'm trying to identify the difference between encodeForHTMLAttribute and encodeForJavaScript. Still, I couldn't find a scenario where untrusted data is used as javascript data values, which broke the code when escaped with encodeForHTMLAttribute, but works securely after escaped using encodeForJavaScript.
I know that for all javascript, its recommended to use encodeForJavaScript. But I like to see the difference.
The answer to your question is boring: The fact is that passing an HTML Entity encoded string to JavaScript is largely an unspecified operation.* JavaScript expects data passed to it to be escaped for JavaScript, with the exception of some API methods, it has no idea what you're sending it.
HTML and JavaScript are different languages. If you'll note, they both have different reserved characters--some the same, meaning they each have reserved characters that make up the language that have to be treated specially when using them in that language.
The correct way to ensure that javascript will always treat incoming code as data, is to escape for JavaScript. Passing it an HTMLEntity encoded String, might work, but we have to say might because that behavior is unspecified. One reason that the question I linked at the beginning partially answers your question is that it is common for JavaScript frameworks to DO that kind of processing on your input... so you better be sure that if that happens, the data is appropriately escaped for JavaScript. Otherwise it will unwrap your HTMLEntity encoding, render and execute script code.
I saved the damning part for last: You can write legal JavaScript with only six characters. And none of these characters are commonly escaped by HTML encoders. Here's an entire guide on using JavaScript escaping like this to evade XSS filters. And for proof that it works, look here.
Or run it yourself in an HTML file on your computer:
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However, if you escape what's between the <script> tags for Javascript... it will be treated purely as data and will not be executed.
*Except for those JavaScript functions that are designed to take HTML-encoded strings as input.
If there is a cookie on our website called cabbages and $.cookie("cabbages") returns this:
"purchaseType":"NONE","futurePurchaseType":"NONE","id":73041988,"unlimitedStatus":null,"hasFuturePrivilege":false,"corpUser":false,"suspendedStatus":null,
What is the prescribed or conventional way to get back the value of id? I want the ID of the visitor so in this example I'd like to write some Javascript that returns 73041988.
Contents of your cabbages cookie looks very close to json object syntax to me. So JSON.parse() would be naturally the way I would take. You just need to add curly braces to that string to make it valid json object syntax.
Actually this has got nothing to do with cookies. If any variable contains data having syntax similar to this, you can always go for JSON.parse() to extract it in to a javascript variable.
Json objects look like:
{name1:value1,name2:value2,name3:value3}
Similarly a json array looks like:
[value1,value2,value3]
and you could use JSON.parse for any data having json sytax.
You can see some more good examples of JSON syntax in links below.
http://json.org/example
http://www.tutorialspoint.com/json/json_syntax.htm
Please note that this JSON API which provides native support for json serialization in javascript may not be available in some older browsers and the function call will fail.
As you mentioned $.cookie() in your question, I guess that your project is already using JQuery. So you better use jQuery.parseJSON(), which makes use of JSON.parse where the browser provides a native implementation, and also provides a fall back parser when browser support is not available.
This Stack Overflow thread has more details about Native JSON support in browsers.
This question already has answers here:
What is the difference between JSON and Object Literal Notation?
(10 answers)
Closed 9 years ago.
I'm a newbie to JS and JSON and trying to understand the difference, I see other threads on this difference but still have few unanswered questions,
I have created 3 objects
Key-vaue pairs in double quotes
Key without quotes but value with quotes
Key-value pairs in single quotes.
Questions.
Asis, is it safe to assume if all the 3 objects are Javascript objects?
How do I determine which one is JSON Object here, when I print the objects in the log, all the objects looks same. Is there a way to determine the JSON Object?
If JSON Objects - key-value pairs are enclosed in double quotes, what does the single quote mean?
Code:
<html>
<head>
<script>
var jsobject = {"fname":"Bob","lname":"Mike"}
console.log(jsobject)
var jsobject = {fname:"Bob",lname:"Mike"}
console.log(jsobject)
var jsobject = {'fname':'Bob','lname':'Mike'}
console.log(jsobject)
</script>
</head>
<body>
</body>
</html>
I think you're confusing syntax and data.
Any number of technologies can have very similar syntax, yet that similar syntax may be used for entirely different purposes, and for creating vastly different data.
when we talk about JSON, we're talking about textual data with a Unicode encoding that follows a character syntax that is meant to be used as a data transferral mechanism. That JSON data can be transferred into a wide variety of different programming environments, parsed, and then converted into actual object structures that make sense for the environment.
The reason that it was named "JavaScript Object Notation" is that its notation is largely patterned after a subset of the literal syntax used in JavaScript programs to create objects and primitive values. Sadly, this naming contributes to the confusion of JavaScript developers.
So to determine if you're dealing with JSON, what's ultimately the most important thing to think about is whether what you're doing will result in the creation of Unicode data that follows the rules of JSON syntax.
Take this example:
var foo = {"bar":"baz"};
Is that JSON? Well if it runs in a JavaScript program, it will be evaluated, and foo will hold a reference to some memory that is not Unicode text data.
Sure we could isolate the {"bar":"baz"} part of the code, and transfer it into its own text file that is encoded as Unicode, but then we're really not dealing with the same example anymore.
So let's say we did that. We open our text editor, make sure it's set up for Unicode encoding, and then paste in that one part of the above code. So now the entirety of our text file is this:
{"bar":"baz"}
Now we can correctly say that we have JSON data. What if I added a ; to the end?
{"bar":"baz"};
It's no longer JSON because it has been corrupted by the ; which is not allowed. Again, we could play around with calling it JSON except for whatever isn't valid, but really it either is or isn't valid in its entirety.
So back to a JavaScript example. Does it every make sense to refer to JSON within the syntax of a JavaScript program? Well take our original example. If we could use some JavaScript syntax to create Unicode data and make it comply with JSON syntax, then yes, we could correctly speak of having JSON in our program.
So does JavaScript let us create Unicode data? Yes, all strings in JavaScript are UTF-16 encoded. Therefore all we need to do is create a string.
var foo = '{"bar":"baz"}';
Now we wouldn't call that entire line JSON, but we could correctly say that the foo variable refers to memory which does hold JSON data.
We could then transfer that data to a server written in an entirely different programming language, and as long as it has a JSON parser, it could parse it, and convert it to whatever object type makes sense to that server.
I'm learning javascript and just noticed that the syntax we use to define objects is the same as the json format. So I'm wondering if they are simply equivalent. Being more precise, does it mean that any javascript object (including its variables and functions) can be translated into json format and the same way around?
JSON is (like it's name "JavaScript Object Notation" indicates) a subset* of the JavaScript syntax, i.e. (nearly) every* JSON is valid JavaScript but not the other way round.
Functions, for example, have no equivalent representation in JSON and therefore, cannot be translated into JSON.
Since the main purpose for JSON is serialization, it doesn't provide representation of statements either.
* There is one exception: more or less all Unicode characters can be written literally in JSON but they must be written using escape sequences in JavaScript. See this blog post for more information. So not every valid JSON is valid JavaScript.
JSON data has only data specified in key-value pairs; where as js objects contain both data and functions enlisted in key-value pairs.
Think of JSON as a string representation of your javascript object. - String being the key word here.
Primarily used for easy transport over HTTP .It is a method created by Douglas Crockford to enable a friendly Javascript data transfer format similar to XML , RSS, et all.
JSON is generally parsed by server and client back into a Javascript object for use.
The following is technically invalid JSON:
{
color: "blue",
size: 14
}
because the property names "color" and "size" are required by the spec to be quoted, i.e.
{
"color": "blue",
"size": 14
}
However, I've noticed that many web services that purport to return "JSON" do not quote their property names, and hardly anybody writing Javascript will quote their property names, since Javascript doesn't require it.
Have there been any proposals to amend or fork JSON to allow unquoted property names? It seems to be a much more natural way of using the format, but I've never seen anything suggesting it should be officially adopted.
The philosophy of the design of JSON appears to be keep it as simple as possible.
"Wrap property names with double quotes" beats "Wrap property names with double quotes, or single quotes, and you can leave the quotes off unless the name includes spaces or other special characters" for simplicity.
I don't think that is likely to change.
Now I'm going to stop before I go off on a rant about HTML5 design philosophy.
I've had trouble with property names that collided with JavaScript reserved words. After fighting with a couple such problems, I keep my JSON heavily quoted when I have the choice. In my opinion, it's much safer.
No, i doubt this will happen. If you are using a web-service that claim to return JSON but do-so invalidly, contact them. You don't fix a specification because people implement it wrong.
And let's not collude our terms, here. Yes, JSON has "JavaScript" in its name, but understand well - JSON is not Javascript.
And before you jump on me and say "But on the json.org site it says JSON is a subset of JavaScript" - yes, I know that.
Yes, technically speaking its JavaScript, but since the format is a) stricly declarative and b) usable outside of the context of JavaScript, it's best to treat it with the mindset that it's not JavaScript. It's just a data format that also happens to be native JavaScript.
Which is why you notice that "JavaScript doesn't require it". Well, that's because JavaScript doesn't, but JSON does. Which is again why I prefer to thing of JSON as "JavaScript, but not really".