Develop Reference

An alternative to eval() or Function() for a two-dimensional array in Javascript? [duplicate]

Given a string of JSON data, how can I safely turn that string into a JavaScript object?
Obviously I can do this unsafely with something like:
var obj = eval("(" + json + ')');
but that leaves me vulnerable to the JSON string containing other code, which it seems very dangerous to simply eval.

JSON.parse(jsonString) is a pure JavaScript approach so long as you can guarantee a reasonably modern browser.

The jQuery method is now deprecated. Use this method instead:
let jsonObject = JSON.parse(jsonString);
Original answer using deprecated jQuery functionality:
If you're using jQuery just use:
jQuery.parseJSON( jsonString );
It's exactly what you're looking for (see the jQuery documentation).

This answer is for IE < 7, for modern browsers check Jonathan's answer above.
This answer is outdated and Jonathan's answer above (JSON.parse(jsonString)) is now the best answer.
JSON.org has JSON parsers for many languages including four different ones for JavaScript. I believe most people would consider json2.js their goto implementation.

Use the simple code example in "JSON.parse()":
var jsontext = '{"firstname":"Jesper","surname":"Aaberg","phone":["555-0100","555-0120"]}';
var contact = JSON.parse(jsontext);
and reversing it:
var str = JSON.stringify(arr);

This seems to be the issue:
An input that is received via Ajax websocket etc, and it will be in String format, but you need to know if it is JSON.parsable. The touble is, if you always run it through JSON.parse, the program MAY continue "successfully" but you'll still see an error thrown in the console with the dreaded "Error: unexpected token 'x'".
var data;
try {
data = JSON.parse(jqxhr.responseText);
} catch (_error) {}
data || (data = {
message: 'Server error, please retry'
});

I'm not sure about other ways to do it but here's how you do it in Prototype (JSON tutorial).
new Ajax.Request('/some_url', {
method:'get',
requestHeaders: {Accept: 'application/json'},
onSuccess: function(transport){
var json = transport.responseText.evalJSON(true);
}
});
Calling evalJSON() with true as the argument sanitizes the incoming string.

If you're using jQuery, you can also use:
$.getJSON(url, function(data) { });
Then you can do things like
data.key1.something
data.key1.something_else
etc.

Just for fun, here is a way using a function:
jsonObject = (new Function('return ' + jsonFormatData))()

$.ajax({
url: url,
dataType: 'json',
data: data,
success: callback
});
The callback is passed the returned data, which will be a JavaScript object or array as defined by the JSON structure and parsed using the $.parseJSON() method.

Using JSON.parse is probably the best way.
Here's an example
var jsonRes = '{ "students" : [' +
'{ "firstName":"Michel" , "lastName":"John" ,"age":18},' +
'{ "firstName":"Richard" , "lastName":"Joe","age":20 },' +
'{ "firstName":"James" , "lastName":"Henry","age":15 } ]}';
var studentObject = JSON.parse(jsonRes);

The easiest way using parse() method:
var response = '{"result":true,"count":1}';
var JsonObject= JSON.parse(response);
Then you can get the values of the JSON elements, for example:
var myResponseResult = JsonObject.result;
var myResponseCount = JsonObject.count;
Using jQuery as described in the jQuery.parseJSON() documentation:
JSON.parse(jsonString);

Try using the method with this Data object. ex:Data='{result:true,count:1}'
try {
eval('var obj=' + Data);
console.log(obj.count);
}
catch(e) {
console.log(e.message);
}
This method really helps in Nodejs when you are working with serial port programming

I found a "better" way:
In CoffeeScript:
try data = JSON.parse(jqxhr.responseText)
data ||= { message: 'Server error, please retry' }
In Javascript:
var data;
try {
data = JSON.parse(jqxhr.responseText);
} catch (_error) {}
data || (data = {
message: 'Server error, please retry'
});

JSON parsing is always a pain. If the input is not as expected it throws an error and crashes what you are doing.
You can use the following tiny function to safely parse your input. It always turns an object even if the input is not valid or is already an object which is better for most cases:
JSON.safeParse = function (input, def) {
// Convert null to empty object
if (!input) {
return def || {};
} else if (Object.prototype.toString.call(input) === '[object Object]') {
return input;
}
try {
return JSON.parse(input);
} catch (e) {
return def || {};
}
};

Parse the JSON string with JSON.parse(), and the data becomes a JavaScript object:
JSON.parse(jsonString)
Here, JSON represents to process JSON dataset.
Imagine we received this text from a web server:
'{ "name":"John", "age":30, "city":"New York"}'
To parse into a JSON object:
var obj = JSON.parse('{ "name":"John", "age":30, "city":"New York"}');
Here obj is the respective JSON object which looks like:
{ "name":"John", "age":30, "city":"New York"}
To fetch a value use the . operator:
obj.name // John
obj.age //30
Convert a JavaScript object into a string with JSON.stringify().

JSON.parse(jsonString);
json.parse will change into object.

JSON.parse() converts any JSON string passed into the function into a JSON object.
To understand it better, press F12 to open "Inspect Element" in your browser and go to the console to write the following commands:
var response = '{"result":true,"count":1}'; //sample json object(string form)
JSON.parse(response); //converts passed string to JSON Object.
Now run the command:
console.log(JSON.parse(response));
You'll get output as an Object {result: true, count: 1}.
In order to use that Object, you can assign it to the variable, maybe obj:
var obj = JSON.parse(response);
By using obj and the dot (.) operator you can access properties of the JSON object.
Try to run the command:
console.log(obj.result);

Official documentation:
The JSON.parse() method parses a JSON string, constructing the JavaScript value or object described by the string. An optional reviver function can be provided to perform a transformation on the resulting object before it is returned.
Syntax:
JSON.parse(text[, reviver])
Parameters:
text
: The string to parse as JSON. See the JSON object for a description of JSON syntax.
reviver (optional)
: If a function, this prescribes how the value originally produced by parsing is transformed, before being returned.
Return value
The Object corresponding to the given JSON text.
Exceptions
Throws a SyntaxError exception if the string to parse is not valid JSON.

If we have a string like this:
"{\"status\":1,\"token\":\"65b4352b2dfc4957a09add0ce5714059\"}"
then we can simply use JSON.parse twice to convert this string to a JSON object:
var sampleString = "{\"status\":1,\"token\":\"65b4352b2dfc4957a09add0ce5714059\"}"
var jsonString= JSON.parse(sampleString)
var jsonObject= JSON.parse(jsonString)
And we can extract values from the JSON object using:
// instead of last JSON.parse:
var { status, token } = JSON.parse(jsonString);
The result will be:
status = 1 and token = 65b4352b2dfc4957a09add0ce5714059

Performance
There are already good answer for this question, but I was curious about performance and today 2020.09.21 I conduct tests on MacOs HighSierra 10.13.6 on Chrome v85, Safari v13.1.2 and Firefox v80 for chosen solutions.
Results
eval/Function (A,B,C) approach is fast on Chrome (but for big-deep object N=1000 they crash: "maximum stack call exceed)
eval (A) is fast/medium fast on all browsers
JSON.parse (D,E) are fastest on Safari and Firefox
Details
I perform 4 tests cases:
for small shallow object HERE
for small deep object HERE
for big shallow object HERE
for big deep object HERE
Object used in above tests came from HERE
let obj_ShallowSmall = {
field0: false,
field1: true,
field2: 1,
field3: 0,
field4: null,
field5: [],
field6: {},
field7: "text7",
field8: "text8",
}
let obj_DeepSmall = {
level0: {
level1: {
level2: {
level3: {
level4: {
level5: {
level6: {
level7: {
level8: {
level9: [[[[[[[[[['abc']]]]]]]]]],
}}}}}}}}},
};
let obj_ShallowBig = Array(1000).fill(0).reduce((a,c,i) => (a['field'+i]=getField(i),a) ,{});
let obj_DeepBig = genDeepObject(1000);
// ------------------
// Show objects
// ------------------
console.log('obj_ShallowSmall:',JSON.stringify(obj_ShallowSmall));
console.log('obj_DeepSmall:',JSON.stringify(obj_DeepSmall));
console.log('obj_ShallowBig:',JSON.stringify(obj_ShallowBig));
console.log('obj_DeepBig:',JSON.stringify(obj_DeepBig));
// ------------------
// HELPERS
// ------------------
function getField(k) {
let i=k%10;
if(i==0) return false;
if(i==1) return true;
if(i==2) return k;
if(i==3) return 0;
if(i==4) return null;
if(i==5) return [];
if(i==6) return {};
if(i>=7) return "text"+k;
}
function genDeepObject(N) {
// generate: {level0:{level1:{...levelN: {end:[[[...N-times...['abc']...]]] }}}...}}}
let obj={};
let o=obj;
let arr = [];
let a=arr;
for(let i=0; i<N; i++) {
o['level'+i]={};
o=o['level'+i];
let aa=[];
a.push(aa);
a=aa;
}
a[0]='abc';
o['end']=arr;
return obj;
}
Below snippet presents chosen solutions
// src: https://stackoverflow.com/q/45015/860099
function A(json) {
return eval("(" + json + ')');
}
// https://stackoverflow.com/a/26377600/860099
function B(json) {
return (new Function('return ('+json+')'))()
}
// improved https://stackoverflow.com/a/26377600/860099
function C(json) {
return Function('return ('+json+')')()
}
// src: https://stackoverflow.com/a/5686237/860099
function D(json) {
return JSON.parse(json);
}
// src: https://stackoverflow.com/a/233630/860099
function E(json) {
return $.parseJSON(json)
}
// --------------------
// TEST
// --------------------
let json = '{"a":"abc","b":"123","d":[1,2,3],"e":{"a":1,"b":2,"c":3}}';
[A,B,C,D,E].map(f=> {
console.log(
f.name + ' ' + JSON.stringify(f(json))
)})
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
This shippet only presents functions used in performance tests - it not perform tests itself!
And here are example results for chrome

Converting the object to JSON, and then parsing it, works for me, like:
JSON.parse(JSON.stringify(object))

The recommended approach to parse JSON in JavaScript is to use JSON.parse()
Background
The JSON API was introduced with ECMAScript 5 and has since been implemented in >99% of browsers by market share.
jQuery once had a $.parseJSON() function, but it was deprecated with jQuery 3.0. In any case, for a long time, it was nothing more than a wrapper around JSON.parse().
Example
const json = '{ "city": "Boston", "population": 500000 }';
const object = JSON.parse(json);
console.log(object.city, object.population);
Browser Compatibility
Is JSON.parse supported by all major browsers?
Pretty much, yes (see reference).

Older question, I know, however nobody notice this solution by using new Function(), an anonymous function that returns the data.
Just an example:
var oData = 'test1:"This is my object",test2:"This is my object"';
if( typeof oData !== 'object' )
try {
oData = (new Function('return {'+oData+'};'))();
}
catch(e) { oData=false; }
if( typeof oData !== 'object' )
{ alert( 'Error in code' ); }
else {
alert( oData.test1 );
alert( oData.test2 );
}
This is a little more safe because it executes inside a function and do not compile in your code directly. So if there is a function declaration inside it, it will not be bound to the default window object.
I use this to 'compile' configuration settings of DOM elements (for example the data attribute) simple and fast.

Summary:
Javascript (both browser and NodeJS) have a built in JSON object. On this Object are 2 convenient methods for dealing with JSON. They are the following:
JSON.parse() Takes JSON as argument, returns JS object
JSON.stringify() Takes JS object as argument returns JSON object
Other applications:
Besides for very conveniently dealing with JSON they have can be used for other means. The combination of both JSON methods allows us to make very easy make deep clones of arrays or objects. For example:
let arr1 = [1, 2, [3 ,4]];
let newArr = arr1.slice();
arr1[2][0] = 'changed';
console.log(newArr); // not a deep clone
let arr2 = [1, 2, [3 ,4]];
let newArrDeepclone = JSON.parse(JSON.stringify(arr2));
arr2[2][0] = 'changed';
console.log(newArrDeepclone); // A deep clone, values unchanged

You also can use reviver function to filter.
var data = JSON.parse(jsonString, function reviver(key, value) {
//your code here to filter
});
For more information read JSON.parse.

Just to the cover parse for different input types
Parse the data with JSON.parse(), and the data becomes a JavaScript object.
var obj = JSON.parse('{ "name":"John", "age":30, "city":"New York"}');
When using the JSON.parse() on a JSON derived from an array, the method will return a JavaScript array, instead of a JavaScript object.
var myArr = JSON.parse(this.responseText);
console.log(myArr[0]);
Date objects are not allowed in JSON.
For Dates do somthing like this
var text = '{ "name":"John", "birth":"1986-12-14", "city":"New York"}';
var obj = JSON.parse(text);
obj.birth = new Date(obj.birth);
Functions are not allowed in JSON.
If you need to include a function, write it as a string.
var text = '{ "name":"John", "age":"function () {return 30;}", "city":"New York"}';
var obj = JSON.parse(text);
obj.age = eval("(" + obj.age + ")");

Another option
const json = '{ "fruit": "pineapple", "fingers": 10 }'
let j0s,j1s,j2s,j3s
console.log(`{ "${j0s="fruit"}": "${j1s="pineapple"}", "${j2s="fingers"}": ${j3s="10"} }`)

Try this. This one is written in typescript.
export function safeJsonParse(str: string) {
try {
return JSON.parse(str);
} catch (e) {
return str;
}
}

Not able to send value to frontend [duplicate]

I must be missing something here, but the following code (Fiddle) returns an empty string:
var test = new Array();
test['a'] = 'test';
test['b'] = 'test b';
var json = JSON.stringify(test);
alert(json);
What is the correct way of JSON'ing this array?

JavaScript arrays are designed to hold data with numeric indexes. You can add named properties to them because an array is a type of object (and this can be useful when you want to store metadata about an array which holds normal, ordered, numerically indexed data), but that isn't what they are designed for.
The JSON array data type cannot have named keys on an array.
When you pass a JavaScript array to JSON.stringify the named properties will be ignored.
If you want named properties, use an Object, not an Array.
const test = {}; // Object
test.a = 'test';
test.b = []; // Array
test.b.push('item');
test.b.push('item2');
test.b.push('item3');
test.b.item4 = "A value"; // Ignored by JSON.stringify
const json = JSON.stringify(test);
console.log(json);

Nice explanation and example above. I found this (JSON.stringify() array bizarreness with Prototype.js) to complete the answer. Some sites implements its own toJSON with JSONFilters, so delete it.
if(window.Prototype) {
delete Object.prototype.toJSON;
delete Array.prototype.toJSON;
delete Hash.prototype.toJSON;
delete String.prototype.toJSON;
}
it works fine and the output of the test:
console.log(json);
Result:
"{"a":"test","b":["item","item2","item3"]}"

I posted a fix for this here
You can use this function to modify JSON.stringify to encode arrays, just post it near the beginning of your script (check the link above for more detail):
// Upgrade for JSON.stringify, updated to allow arrays
(function(){
// Convert array to object
var convArrToObj = function(array){
var thisEleObj = new Object();
if(typeof array == "object"){
for(var i in array){
var thisEle = convArrToObj(array[i]);
thisEleObj[i] = thisEle;
}
}else {
thisEleObj = array;
}
return thisEleObj;
};
var oldJSONStringify = JSON.stringify;
JSON.stringify = function(input){
if(oldJSONStringify(input) == '[]')
return oldJSONStringify(convArrToObj(input));
else
return oldJSONStringify(input);
};
})();

Another approach is the JSON.stringify() replacer function param. You can pass a 2nd arg to JSON.stringify() that has special handling for empty arrays as shown below.
const arr = new Array();
arr.answer = 42;
// {"hello":"world","arr":{"answer":42}}
JSON.stringify({ hello: 'world', arr }, function replacer(key, value) {
if (Array.isArray(value) && value.length === 0) {
return { ...value }; // Converts empty array with string properties into a POJO
}
return value;
});

Alternatively you can use like this
var test = new Array();
test[0]={};
test[0]['a'] = 'test';
test[1]={};
test[1]['b'] = 'test b';
var json = JSON.stringify(test);
alert(json);
Like this you JSON-ing a array.

Json has to have key-value pairs. Tho you can still have an array as the value part. Thus add a "key" of your chousing:
var json = JSON.stringify({whatver: test});

turn typescript object into json string

I'm trying to initialize an object in typescript which requires a JSON string for the "options" parameter. To be precise it is the object here. The options parameter is required to be a JSON string and not an object for initializing the dijit.
Is there a way to create a JSON string from a typescript object without it being a manual process?
Please DO NOT link any questions which don't specifically say "TypeScript" as this question specifically relates to TypeScript. While a derivative of JavaScript the way that you write code is different and therefore this is the only post asking this question currently relating to TypeScript.

Just use JSON.stringify(object). It's built into Javascript and can therefore also be used within Typescript.

TS gets compiled to JS which then executed. Therefore you have access to all of the objects in the JS runtime. One of those objects is the JSON object. This contains the following methods:
JSON.parse() method parses a JSON string, constructing the JavaScript value or object described by the string.
JSON.stringify() method converts a JavaScript object or value to a JSON string.
Example:
const jsonString = '{"employee":{ "name":"John", "age":30, "city":"New York" }}';
const JSobj = JSON.parse(jsonString);
console.log(JSobj);
console.log(typeof JSobj);
const JSON_string = JSON.stringify(JSobj);
console.log(JSON_string);
console.log(typeof JSON_string);

You can use the standard JSON object, available in Javascript:
var a: any = {};
a.x = 10;
a.y='hello';
var jsonString = JSON.stringify(a);

Be careful when using these JSON.(parse/stringify) methods. I did the same with complex objects and it turned out that an embedded array with some more objects had the same values for all other entities in the object tree I was serializing.
const temp = [];
const t = {
name: "name",
etc: [{
a: 0
}],
};
for (let i = 0; i < 3; i++) {
const bla = Object.assign({}, t);
bla.name = bla.name + i;
bla.etc[0].a = i;
temp.push(bla);
}
console.log(JSON.stringify(temp));

If you're using fs-extra, you can skip the JSON.stringify part with the writeJson function:
const fsExtra = require('fs-extra');
fsExtra.writeJson('./package.json', {name: 'fs-extra'})
.then(() => {
console.log('success!')
})
.catch(err => {
console.error(err)
})

How to retrieve particular data from JSON file using jQuery

I am trying to read JSON file stored locally in my system using jQuery. I want to get some particular data from that file. Let's suppose the file looks like as below:
{"statements":[{"subject":{"uriString":"A","localNameIdx":-1},
"predicate":{"uriString":"B","localNameIdx":-1},
"object":{"uriString":"C"}}
This is what has been written by Java program. My question is: How can I retrieve the following dataA, B and Cfrom this file using jQuery? My code to read JSON file is:
var arr = [];
$.getJSON("/Users/docs/sample.json", function(data) {
$.each(data.statements, function(i, val) {
arr.push(val);
}
}
The code does not retrieve A, B and C. Could anyone please help me how to get these elements and store them in an array in jQuery. Your help would be very much appreciated.

OK. Bare in mind JSON (JavaScript Object Notation) is just a JavaScript Object, with a funny coat on. So if you have a JSON string, and Jquery, you can use the parseJSON method to rehydrate the string into to the object is really represents.
Such as...
var obj = jQuery.parseJSON( '{ "name": "John" }' );
alert( obj.name === "John" );

You should try something like this
$.each(data.statements[0], function(i, v){
// arr.push(v.uriString);
console.log(v.uriString); // will print A B C
});
But, in this case, your object should look like this
var data = {
"statements":[
{
"subject":{"uriString":"A","localNameIdx":-1},
"predicate":{"uriString":"B","localNameIdx":-1},
"object":{"uriString":"C","localNameIdx":-1}
}
] // <-- mising in your question
}; // <-- mising in your question
In your question, I didn't find the closing ]}, I think it was a typo, check this example.

You're only looping through data.statements. This only gives you one item, data.statements.subject, which is {"uriString":"A","localNameIdx":-1}
It appears you want to get the uriString of every item, regardless of how nested that item is. To do this, it'd be easiest to define a recursive function.
function getUriStrings( obj ){
var results = [];
for(var key in obj){
if(key == "uriString"){
results.push(obj[key]);
}
else if(obj[key] != null && typeof obj[key] === 'object'){
results.push.apply(results, getUriStrings(obj[key]));
}
}
return results;
}
Then your code will just be:
var arr = [];
$.getJSON("/Users/docs/sample.json", function(data) {
arr = getUriStrings( data );
}

JSON.stringify() only allows one value parameter. How do I add more parameters to be stringified under one brace?

http.get(options, function(res){
fs.appendFile('log.txt', JSON.stringify(res.headers, null, 4));
})
I have a question regarding the JSON.stringify() function.
I've learned that simply using the res.headers does not in fact output to JSON format.
At the moment, I am restricted to only being able to use one res.xxxxx method within JSON.stringify(). The piece of code in question is pasted above. How am I able to use more than one value? At the moment, I can only put in res.headers into the value parameter. I would also like to use res.statusCode and my own objects, all stringified under one brace {}.
The parameters of JSON.Stringify is as follows: JSON.stringify(value, [replacer], [space]);

You need to create a new js object and put res.headers into it.
var obj = {};
obj.headers = res.headers;
obj.somethingelse = somethingelse;
var string = JSON.stringify(obj);

JSON is always a single value. So the output out JSON.stringify can always only be a single value. It would make sense to have the input be a single value too. This is like asking why can't my function return two things? You can make it return some composite value, but that means you're still returning a single (composite) value. The solution here is the same, compose your input.
var reply = {
code: res.statusCode,
headers: parse_http_headers(res.headers),
etc: /* etc */
};
log(JSON.stringify(reply));
Note that you must write parse_http_headers yourself.

You could always add the extra things you want to the headers object...
res.headers.statusCode = res.statusCode
JSON.stringify(res.headers, null, 4);
I don't know if there are any bad side effects if you mutate the res object in node. You might want to consider creating a shallow copy of the headers object if you are worried about that.

You could as well stringify more than only the headers part of your object:
JSON.stringify(res, …)
If you want to stringify only certain parts of your object, you can
filter them with the replacer function,
delete everything else before,
or build a new object to be stringified:
JSON.stringify({
heads: res.headers,
…
}, …)

If you'd like to flatten several objects, you can use this function.
function merge() {
var out = {};
insert = function(e) {
for (var i in e) {
if (Object.prototype.hasOwnProperty.call(e, i))
out[i] = e[i];
}
};
for (var i = 0; i < arguments.length; i++) {
insert(arguments[i]);
}
return out;
}
var a = {'a': 'aa'};
var b = {'b': 'bb', 'bbb': 'bbbb'};
var c = {'c': 'cc'};
var combined = merge(a,b,c);