Develop Reference

Why JSON.parse fails with this array-like string

I tried to JSON parse this
let string = `["\"test1, "\"test2"]`;
let array = JSON.parse(string);
console.log(array[0]);
It's fairly simple enough but I don't understand what's error message is supposed to tell
Uncaught SyntaxError: Unexpected token t in JSON at position 3

you are using template string to create a string.
it doesnt need a escape character for double quotes ".
type this:
let string = `["test1", "test2"]`;
let array = JSON.parse(string);
console.log(array[0])
you need a escape character for " only when you are using normal string. like this:
let string = "[\"test1\", \"test2\"]";
let array = JSON.parse(string);
console.log(array[0])
im not good at english.hope useful

Javascript - Parse a stringified arrays of strings

I have a string like so :
a= "['url1','url2','url3']"
coming from the server I want to convert it to array like :
arr = ["url1","url2","url3"]
but JSON.parse does not seems to be working and gives following error:
SyntaxError: Unexpected token ' in JSON at position 1
Thanks in advance.

You need to replace the single quotes with double quotes. An easy way to achieve this can be by replacing them with escaped quotes like this:
let validJSON = a.replace(/'/g, "\"")
JSON.parse(validJSON)

Your string needs to be in single quotes for JSON.parse to work in this example, also string representation in json uses double quotes as per standard.
JSON.parse('["url1","url2","url3"]')

Try to use this code:
a = "['url1','url2','url3']"
urls = a.split(',')
arr = urls.map(url => url.replace(/'|\[|\]/g, ''))
console.log(arr) // ["url1", "url2", "url3"]
https://jsfiddle.net/z1frh8ys/

Converting array inside a string to an array

I have a response which contains an array which is present inside string(""). What I need I just the array. How do I get rid of the quotes?
I tried JSON.parse(). It gave me error message
SyntaxError: Unexpected token ' in JSON at position 1
What I have is as follows:
email_id: "['abc#mail.com', 'cde#mail.com']"
What I need is as follows:
email_id: ['abc#mail.com', 'cde#mail.com']
This is a key which a part of a large response I am getting from backend in my angular 7 app.

Below solution will work for your case provided the strings does not contain /'
var a = "['abc#mail.com', 'cde#mail.com', 'def#mail.com']";
a = a.replace(/'/g, '"');
var result = JSON.parse(a);
Considering its an email data, there's no possibility of having that escape character sequence

You have to send in backend the format with double quotes instead of one quotes or in front just replace quotes ' with double quotes " inside your array , otherwise the parse will fail ,
see below snippet :
let json = {
email_id: "['abc#mail.com', 'cde#mail.com']"
}
json.email_id = json.email_id.replace(/'/g,"\"");
console.log(JSON.parse(json.email_id));

How do JSON.parse() and escape characters work in JavaScript?

Suppose I have an object variable:
var obj = {
key: '\"Hello World\"'
}
Then I tried parse it to string by using JSON.stringify in Chrome devtools console:
JSON.stringify(obj) // "{"key":"\"Hello World\""}"
I get the result "{"key":"\"Hello World\""}". Then I give it to a string
var str = '{"key":"\"Hello World\""}'
At least I try to convert it back to obj:
JSON.parse(str);
but the browser tell me wrong Uncaught SyntaxError
What confused me is why this is wrong? I get the string from an origin object and I just want turn it back.
How can I fix this problem? If I want do the job like convert obj to string and return it back, how can I do?

You're tried to convert your JSON into a string literal by wrapping it in ' characters, but \ characters have special meaning inside JavaScript string literals and \" gets converted to " by the JavaScript parser before it reaches the JSON parser.
You need to escape the \ characters too.
var str = '{"key":"\\"Hello World\\""}'
That said, in general, it is better to not try to embed JSON in JavaScript string literals only to parse them with JSON.parse in the first place. JSON syntax is a subset of JavaScript so you can use it directly.
var result = {"key":"\"Hello World\""};

try:
var str = '{"key":"\\"Hello World\\""}';

JSON.stringify escapes double quotes every time when stringified

I am storing JSON objects retreived from web service to objects in javascript. In many places this gets stringified(This obj goes through some plugins and it strigifies and stores it and retreives it) and it adds multiple slashes. How can I avoid it ?
http://jsfiddle.net/MJDYv/2/
var obj = {"a":"b", "c":["1", "2", "3"]};
var s = "";
console.log(obj);
s = JSON.stringify(obj);
alert(s); // Proper String
s = JSON.stringify(s);
alert(s); // Extra slash added, Quotes are escaped
s = JSON.stringify(s);
alert(s); // Again quotes escaped or slash escaped but one more slash gets added
var obj2 = JSON.parse(s);
console.log(obj2); // Still a String with one less slash, not a JSON object !
So when parsing this multiple string I end up with a string again. And when tried to access like an object it crashes.
I tried to remove slash by using replace(/\\/g,"") but I end with this : ""{"a":"b","c":["1","2","3"]}""

What did you expect to happen?
JSON.stringify does not act like an "identity" function when called on data that has already been converted to JSON. By design, it will escape quote marks, backslashes, etc.
You need to call JSON.parse() exactly as many times as you called JSON.stringify() to get back the same object you put in.

Try
JSON.stringify(s).replace(/\\"/g, '"')

You can avoid that simply by calling JSON.stringify() exactly once on the data you want turn into JSON.

Try this:
s = {"a":"b", "c":["1", "2", "3"]}
JSON.stringify(JSON.stringify(s))
gives the output as
'"{\"a\":\"b\",\"c\":[\"1\",\"2\",\"3\"]}"'