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How do we make JavaScript think that a string is JSON?

I have a function which only works if JSON object is passed to it. If I pass a string to it, with same format as JSON, it doesnt work. So I want to make that function think that the string passed to it is a JSON. The string is indeed in the JSON format.
I also tried the following. I inputted the string through Ajax , with "handle as" parameter as "JSON", and then when I passed the result to the function it works.
So I deduced the problem is not with the string. How do i convert this string to JSON? If i get same string through ajax request and then passing it to function works, whereas directly passing it doesnt work.
Screenshot of console log:
Advance Thanks

JavaScript is a dynamically typed language, so you can't really specify types of function arguments up front. If you want that, look into TypeScript.
JSON is nothing but a String, not a standalone type in JavaScript. To convert a JavaScript object to the equivalent JSON string representation use:
const myJSON = JSON.stringify ({ a: 'b' })
To get a JavaScript object back from a JSON string use:
JSON.parse (myJSON)
When going over the network, libraries can automatically return serialized objects if you specify the type as JSON. You haven't pasted any code, so I'm guessing that you haven't specified application/json as the Content-Type in your network request. Since you've tagged your question jQuery, take a look at [$.getJSON][2], this should do what you want.

Use JSON.parse
function isJson(str) {
try {
JSON.parse(str);
} catch (e) {
return false;
}
return true;
}
Example:
function isJson(str) {
try {
JSON.parse(str);
} catch (e) {
return false;
}
return true;
}
str = '{"a":1, "b":2}';
console.log(isJson(str)); // true
str1 = '{["a":1, "b":2]}';
console.log(isJson(str1)); // false

How to retrieve value from json of one array and one int literal in javascript

I am passing data back to java script through a rest api. The rest API return data in the following below mentioned structure.I am confused what format of json is it and how can i iterate on the array inside and get the int value individually.
The format of my response is like :
{"searchOrder":[
{"location":"10","trackingId":"656"},
{"location":"34","trackingId":"324"},....],
"count":100}
i want searchOrder as array of json to display in table and count to show total row.How can i get them?

Just iterate over the array and extract the values
// Turn the JSON into a JS object (maybe in your XHR handler)
var data = JSON.parse(jsonString); // jsonString could be responseText from XHR
var arrayOfTrackingIdValues = data.searchOrder.map(function (value) {
return value.trackingId;
});

JavaScript provide built-in function JSON.parse() to convert the string into a JavaScript object and drive/iterate the each element based on type obj/array
var obj = JSON.parse(text);

Json associative array accessing in jQuery

I am getting response in below format for every product and in a single call there can be many products. I am trying to access this data via jQuery but I'm not able to access it.
Productdata['someid'] = { "Product Json data"}
I am using below syntax in jQuery but not getting the data. Please suggest.
alert(Productdata['someid']);

Its not going as JSON format .
JSON is a key : value pair format ;
so your Productdata should be in below format:
Productdata = { 'someid' : "Product Json data"}

A Json like this
var data={"name":"somebody"};
To call
return data.name
Or
return data["name"]

The problem here is that JavaScript does not support associative arrays (scroll down to "Associative arrays, no way!"). It has some internal workarounds which make it appear as if it does, but really all it does is just adding the keys as properties.
So you would most likely be able to access it using Productdata.someid = ....
EDIT:
So assuming you have the following JSON string: {"id":"123"} (which is valid JSON), you can use it like this:
var jsonString = '{"id":"123"}';
var parsedJSON = $.parseJSON(jsonString);
var productID = "product_" + parsedJSON.id;
Does this help?
Some useful links: JSON format checker to make sure the JSON is valid.
Unfortunately I wasn't allowed to add more than 2 links, so the jQuery parseJSON function link is still in the comment below.

Javascript: Parse JSON output result

How can i retrieve the values from such JSON response with javascript, I tried normal JSON parsing seem doesn't work
[["102",true,{"username":"someone"}]]
Tried such codes below:
url: "http://somewebsite.com/api.php?v=json&i=[[102]]",
onComplete: function (response) {
var data = response.json[0];
console.log("User: " + data.username); // doesnt work

var str = '[["102",true,{"username":"someone"}]]';
var data = JSON.parse(str);
console.log("User: " + data[0][2].username);
Surround someone with double quotes
Traverse the array-of-array before attempting to acces the username property
If you are using AJAX to obtain the data, #Alex Puchkov's answer says it best.

So the problem with this is that it looks like an array in an array. So to access an element you would do something like this.
console.log(obj[0][0]);
should print 102
Lets say you created the object like so:
var obj = [["102",true,{"username":someone}]];
this is how you would access each element:
obj[0][0] is 102
obj[0][1] is true
and obj[0][2]["username"] is whatever someone is defined as
From other peoples answers it seems like some of the problem you may be having is parsing a JSON string. The standard way to do that is use JSON.parse, keep in mind this is only needed if the data is a string. This is how it should be done.
var obj = JSON.parse(" [ [ "102", true, { "username" : someone } ] ] ")

It depends on where you are getting JSON from:
If you use jQuery
then jQuery will parse JSON itself and send you a JavaScript variable to callback function. Make sure you provide correct dataType in $.ajax call or use helper method like $.getJSON()
If you getting JSON data via plain AJAX
then you can do:
var jsonVar = JSON.parse(xhReq.responseText);

How to retrieve value from object in JavaScript

Hi I am using a Java script variable
var parameter = $(this).find('#[id$=hfUrl]').val();
This value return to parameter now
"{'objType':'100','objID':'226','prevVoting':'" // THIS VALUE RETURN BY
$(this).find('[$id=hfurl]').val();
I want to store objType value in new:
var OBJECTTYPE = //WHAT SHOULD I WRITE so OBJECTTYPE contain 400
I am trying
OBJECTTYPE = parameter.objType; // but it's not working...
What should I do?

Try using parameter['objType'].
Just a note: your code snippet doesn't look right, but I guess you just posted it wrong.

Ok, not sure if I am correct but lets see:
You say you are storing {'objType':'100','objID':'226','prevVoting':' as string in a hidden field. The string is not a correct JSON string. It should look like this:
{"objType":100,"objID":226,"prevVoting":""}
You have to use double-quotes for strings inside a JSON object. For more information, see http://json.org/
Now, I think with $(this).find('[$id=hfurl]'); you want to retrieve that value. It looks like you are trying to find an element with ID hfurl,but $id is not a valid HTML attribute. This seems like very wrong jQuery to me. Try this instead:
var parameter = $('#hfurl').val();
parameter will contain a JSON string, so you have to parse it before you can access the values:
parameter = $.parseJSON(parameter);
Then you should be able to access the data with parameter.objType.
Update:
I would not store "broken" JSON in the field. Store the string similar to the one I shoed above and if you want to add values you can do it after parsing like so:
parameter.vote = vote;
parameter.myvote = vote;
It is less error prone.