Best practice for converting string to object in JavaScript

Question

I am working on a small UI for JSON editing which includes some object and string manipulation. I was able to make it work, but one of the fields is bit tricky and I would be grateful for an advice. Initial string:

 'localhost=3000,password=12345,ssl=True,isAdmin=False' 

Should be converted to this:

{ app_server: 'localhost:3000', app_password:'12345', app_ssl: 'True', app_isAdmin: 'False' }

I was able to do that by first splitting the string with the ',' which returns an array. And then I would loop through the second array and split by '='. In the last step I would simply use forEach to loop through the array and create an object:

  const obj = {}
  arr2.forEach((item) => (obj[`app_${item[0]}`] = item[1]));

This approach works, but in case some of the fields, i.e password contains ',' or '=', my code will break. Any idea on how to approach this? Would some advanced regex be a good idea?

Edit: In order to make things simple, it seems that I have caused an opposite effect, so I apologize for that.

The mentioned string is a part of larger JSON file, it is the one of the values. On the high level, I am changing the shape of the object, every value that has the structure I described 'server='something, password=1234, ssl=True', has to be transformed into separate values which will populate the input fields. After that, user modify them or simply download the file (I have separate logic for joining the input fields into the initial shape again)

Answer 1

Observation/Limitation with the design that you have :

• As per your comment, none of the special characters is escaped in any way then how we will read this string password=12345,ssl=True ? It will be app_password: 12345,ssl=True or app_password: 12345 ?
• why localhost=3000 is converted into app_server: 'localhost:3000' instead of app_localhost: '3000' like other keys ? Is there any special requirement for this ?
• You have to design your password field in the way that it will not accept at least , character which is basically used to split the string.

Here you go, If we can correct the above mentioned design observations :

const str = 'localhost=3000,password=123=45,ssl=True,isAdmin=False';


const splittedStr = str.split(',');

const result = {};

splittedStr.forEach(s => {
  const [key, ...values] = s.split('=')
  const value = values.join('=');
  result[`app_${key}`] = value
});

console.log(result);

As you can see in above code snippet, I added password value as 123=45 and it is working properly as per the requirement.

Answer 2

You can use a regular expression that matches key and value in the key=value format, and will capture anything between single quotes when the value happens to start with a single quote:

(\w+)=(?:'((?:\\.|[^'])*)'|([^,]+))

This assumes that:

• The key consists of alphanumerical characters and underscores only
• There is no white space around the = (any space that follows it, is considered part of the value)
• If the value starts with a single quote, it is considered a delimiter for the whole value, which will be terminated by another quote that must be followed by a comma, or must be the last character in the string.
• If the value is not quoted, all characters up to the next comma or end of the string will be part of the value.

As you've explained that the first part does not follow the key=value pattern, but is just a value, we need to deal with this exception. I suggest prefixing the string with server=, so that now also that first part has the key=value pattern.

Furthermore, as this input is part of a value that occurs in JSON, it should be parsed as a JSON string (double quoted), in order to decode any escaped characters that might occur in it, like for instance \n (backslash followed by "n").

Since it was not clarified how quotes would be escaped when they occur in a quoted string, it remains undecided how for instance a password (or any text field) can include a quote. The above regex will require that if there is a character after a quote that is not a comma, the quote will be considered part of the value, as opposed to terminating the string. But this is just shifting the problem, as now it is impossible to encode the sequence ', in a quoted field. If ever this point is clarified, the regex can be adapted accordingly.

Implementation in JavaScript:

const regex = /(\w+)=(?:'(.*?)'(?![^,])|([^,]+))/g;

function parse(s) {
    return Object.fromEntries(Array.from(JSON.parse('"server=' + s + '"').matchAll(regex), 
        ([_, key, quoted, value]) => ["app_" + key, quoted ?? (isNaN(value) ? value : +value)]
    ));
}

// demo:
//     Password includes here a single quote and a JSON encoded newline character
const s = "localhost:3000, password='12'\\n345', ssl='True', isAdmin='False'";
console.log(parse(s));