Using regular expressions, eliminate the element from a JSON object that contains a specified property

Imagine I have a string representing a JSON object. It could be invalid, with some params that will be replaced by another system (e.g. %param%). The task at hand is to remove all objects with a known propertyName equal to "true" using regex.

{
    "someTopLevelProp": "value",
    "arrayOfData": [
        {
            "firstPropIAlwaysKnow": "value",
            "dontCareProp": $paramValue$,
            "dontCareProp2": 2,
            "flagWhichShouldIUse": true,
            "somethingAtTheEnd": "value"
        },
        {
            "absolutelyAnotherObject": %paramValue%
        },
        {
            "firstPropIAlwaysKnow": "value",
            "dontCareProp": "value",
            "dontCareProp2": 2,
            "flagWhichShouldIUse": false,
            "somethingAtTheEnd": "value"
        },
        {
            "firstPropIAlwaysKnow": "value",
            "dontCareProp": "value",
            "dontCareProp2": 2,
            "flagWhichShouldIUse": true,
            "somethingAtTheEnd": "value"
        }
    ]
}

In the scenario above, there's always "firstPropIAlwaysKnow" which indicates that the object may contain the flag that needs removal. Subsequent properties may follow. The crucial factor is "flagWhichShouldIUse", signifying the object for deletion (only if value is 'true'). The desired result should be:

{
    "someTopLevelProp": "value",
    "arrayOfData": [
        {
            "absolutelyAnotherObject": %paramValue%
        },
        {
            "firstPropIAlwaysKnow": "value",
            "dontCareProp": "value",
            "dontCareProp2": 2,
            "flagWhichShouldIUse": false,
            "somethingAtTheEnd": "value"
        }
    ]
}

My regex skills are not proficient enough, so seeking help from the community.

P.S. Refrain from stating that parsing JSON with regex is a crazy\incorrect\bad idea - rest assured, I am aware of that.

ANSWER: I now possess a functional regex that accomplishes the task. Gratitude to everyone who offered assistance. It may prove beneficial to others as well.

/{\s+?"firstPropIAlwaysKnow": "value"[^{}]+?(?:\{[^}]*\}[^}]+?)*[^}]+?"flagWhichShouldIUse": true[^}]+?},?/gi

Regexper

Answer №1

Solely relying on regular expressions is not sufficient for this particular task. A potential solution could involve:

let filteredData = jsonDataString
  // segment the content into individual 'objects'
  // the method of splitting may need adjustments based on formatting.
  // Consider splitting using something like /},\s*{/,
  // but reassembling with the same formatting could be challenging
  .split('},{')
  // keep only the strings with the specified property set to false
  .filter(str => str.match(/"desiredFlag":\s*false/) // modify as necessary
   // reconstruct the original format
  .join('},{');

The way you break down the data will heavily depend on your JSON structure, and this approach has its limitations. It does not handle nesting accurately. If your JSON is well-formatted, incorporating the number of indentation characters in the splitter might help: For instance, a single tab could be represented as follows:

/\n\t},\s*{/<code></p>
    </div></answer1>
<exanswer1><div class="answer accepted" i="40635659" l="3.0" c="1479298440" m="1479310348" v="3" a="SmFyZWQgU21pdGg=" ai="3757232">
<p>You really can't do this with just regular expressions. Something like this might work:</p>

<pre><code>let filtered = jsonstring
  // split into the individual 'objects'
  // might need to modify this depending on formatting. You
  // could use something like /},\s*{/ to split the string,
  // but couldn't re-join with same formatting
  .split('},{')
  // filter for only the strings with the relevant property
  // set to false
  .filter(s => s.match(/"flagWhichShouldIUse":\s*false/) // again, may need to change
   // put humpty-dumpty back together again
  .join('},{');

The exact splitting method will depend heavily on the structure of your JSON, and this isn't fool-proof. It doesn't handle nesting properly. If your JSON is pretty-printed, you could use the number of tab/space characters as part of the splitter: this for instance would only split for one tab only: /\n\t},\s*{/

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