JavaScript - Extract JSON from log file

Question

I need to extract JSON string (which will be used later to parse JSON) from a log file. The file is in this format:

[16:11:20] some text
[16:11:20] some text
some text
some text
[
  {
    "description": "some text",
    "elements": [{
        "id": "some text",
        "keyword": "some text",
        "line": 20,
        "name": "some text",
        "steps": [{
            "arguments": [],
            "keyword": "some text ",
            "result": {
                "status": "passed",
                "duration": 14884761888
            },
            "hidden": true,
            "match": {
                "location": "some text"
            }
        },
        {
            "arguments": [],
            "keyword": "sometext ",
            "name": "sometext",
            "result": {
                "status": "passed",
                "duration": 463674
            },
            "line": 11,
            "match": {
                "location": "sometext"
            }
        }
        ],
        "tags": [
          {
            "name": "@sometext-no",
            "line": 7
          },
          {
            "name": "@sometext",
            "line": 8
          }
        ],
        "type": "sometext"
      }

    ],
    "id": "sometext",
    "keyword": "sometext",
    "line": 1,
    "name": "sometext",
    "tags": [],
    "uri": "sometext"
  }
][16:11:54] some text
[16:11:54] some text

How can I construct a regex in JavaScript which will extract JSON data from this file so that it can be used by string.match() to give the desired output

The pattern I am trying is as below

var regExtract = /(\[\s+\{[\s\S]*\}\s+\]\s+\}\s+\]\s+\}\s+\])/;
var matchedJson = data.toString().match(regExtract)[1];

So, is that pattern not working? Note that \s+ means "one or more whitespace characters", so that means your pattern will not match your example. You also have the end of your pattern, }] several times. — Heretic Monkey
– Heretic Monkey, Commented Jul 19, 2016 at 20:15
Here's a patter which matches the provided format: regex101.com/r/uU9oI0/1 — David Horák
– David Horák, Commented Jul 19, 2016 at 20:17
Would that "json" data string always be placed on a separate line? — RomanPerekhrest
– RomanPerekhrest, Commented Jul 19, 2016 at 20:24
updated the qs with sample log file from which JSON is to be extracted — Manya
– Manya, Commented Jul 19, 2016 at 22:37

Alex K · Accepted Answer · 2016-07-20 13:33:59Z

2

I update my answer, you can try something like that:

var str = `[16:11:20] some text
[16:11:20] some text
some text
some text
[
  {
    "description": "some text",
    "elements": [{
        "id": "some text",
        "keyword": "some text",
        "line": 20,
        "name": "some text",
        "steps": [{
            "arguments": [],
            "keyword": "some text ",
            "result": {
                "status": "passed",
                "duration": 14884761888
            },
            "hidden": true,
            "match": {
                "location": "some text"
            }
        },
        {
            "arguments": [],
            "keyword": "sometext ",
            "name": "sometext",
            "result": {
                "status": "passed",
                "duration": 463674
            },
            "line": 11,
            "match": {
                "location": "sometext"
            }
        }
        ],
        "tags": [
          {
            "name": "@sometext-no",
            "line": 7
          },
          {
            "name": "@sometext",
            "line": 8
          }
        ],
        "type": "sometext"
      }

    ],
    "id": "sometext",
    "keyword": "sometext",
    "line": 1,
    "name": "sometext",
    "tags": [],
    "uri": "sometext"
  }
][16:11:54] some text
[16:11:54] some text
`;

var json = '';
var jsonArray = [];
var implode = false;
str.split('\n').forEach(function(v, k){   
  if(v === '  {'){
    console.log(k, v);
    implode = true;
  }

  if(implode){
    json = json + v + '\n';
  }

  if(v === '  }'){      
    console.log(k, v);
    implode = false;
    jsonArray.push(json.trim());
    json = '';

    console.log(jsonArray);    
  }
});
console.log(JSON.parse(jsonArray[0]));

Fiddle: https://jsfiddle.net/x0cc25q4/7/

UPDATE: Short version with regex:

var arr = str.split('\n').join('').match(/\[\s{2}(\{.*?\})\]/g);
console.log(JSON.parse(arr[0]));

Fiddle: https://jsfiddle.net/x0cc25q4/8/

edited Jul 20, 2016 at 13:33

answered Jul 19, 2016 at 20:46

Alex K

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3 Comments

Manya Over a year ago

This solution is fine but I was wondering if there is any regex way of doing it as that would reduce the code drastically.

Alex K Over a year ago

Extremely short version for you :)

Alex K Over a year ago

Glad it worked ! Please accept the answer as it would help others who have the same question, thank you :)

SvenT · Accepted Answer · 2016-07-19 20:24:48Z

1

not sure this works with regexp only since you need to count opening and closing brackets. try

var start=string.indexOf('[{');
var level=1;
start++;
while (level>0){
   if (string[start]==='[') level++;
   if (string[start]===']') level--;
   start++;
}

this surely gets more complicated if there could be '[' or ']' within strings in the json.

answered Jul 19, 2016 at 20:24

SvenT

113 bronze badges

1 Comment

Whothehellisthat Over a year ago

You also need to count opening/closing curly braces, in case there are nested objects.

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