Need help in formatting JSON (in JavaScript) with Stringify and Regex replace

Question

I am missing something with the regex and it's removing the last letter of each item before the comma.

Sample code:

let test_json = { 
    "a" : { "a1" : "one", "is_active" : true, "a2" : "two" },
    "b" : { "b1" : "one", "is_active" : true, "b2" : "two" } 
}; 

JSON.stringify(test_json, null, 3).replace(/[^}],\n( )*"/g, ',   "');

The result is:

"{
   "a": {
      "a1": "one,   "is_active": tru,   "a2": "two"
   },
   "b": {
      "b1": "one,   "is_active": tru,   "b2": "two"
   }
}"

What I am trying to get is:

"{
   "a": {
      "a1": "one",   "is_active": true,   "a2": "two"
   },
   "b": {
      "b1": "one",   "is_active": true,   "b2": "two"
   }
}"

The things that are wrong:
"one, should be "one",
"tru, should be "true",

"Text that's matched inside a non-capturing group is still consumed, the same as text that's matched outside of any group. A capturing group is like a non-capturing group with extra functionality: in addition to grouping, it allows you to extract whatever it matches independently of the overall match." - From: stackoverflow.com/questions/7505762/… — evolutionxbox
– evolutionxbox, Commented Jan 18, 2021 at 23:29

Ben Wainwright · Accepted Answer · 2021-01-18 23:42:37Z

3

Your problem is that you are finding the following sequence of characters

Any character that is not a closing brace
A comma
A newline character
Any number of spaces

And replacing the entire sequence. Since the "e" on the end of "true" is not a closing brace, it gets replaced as well.

What you need is for the first item in the sequence to be "a comma that comes immediately after a closing brace". You can do this using a negative lookbehind.

let test_json = {
  a: {
    a1: "one",
    is_active: true,
    a2: "two"
  },
  b: {
    b1: "one",
    is_active: true,
    b2: "two"
  },
};

const result = JSON.stringify(test_json, null, 3).replace(
  /(?<!}),\n\s*/g,
  ", "
);

console.log(result);

edited Jan 18, 2021 at 23:42

answered Jan 18, 2021 at 23:36

Ben Wainwright

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MCP · Accepted Answer · 2021-01-18 23:31:07Z

1

JSON.stringify(test_json,null,3).replace(/([^}]?),\n( )*"/g, '$1,   "');

not sure of it's the best way but it's the first thing that came to mind

answered Jan 18, 2021 at 23:31

MCP

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1 Comment

Pranav Shah Over a year ago

Thanks, but this does not work for me as it messes up the formatting for "b", which should come on a new line

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