what is a reliable way to validate if this string is valid json?

Question

I'm working on an app where a function needs to validate if a provided string parameter is valid json. But the function also needs to handle JSON which has been copied from jira. For example, the json could look like this:

"{
    "query": {
        "size": 0,
        "aggregations": {
            "ipTag": {
                "terms": {
                    "field": "ipTag",
                    "size": 1001
                }
            }
        }
    },
    "table": "ip_info_table"
}"

Not sure if the following format of the string param is becuase it was copied/pasted from Jira, or if it has to do with MUI Input controls. But anyway, this is what the format looks like when I copy/paste the variable into a CDT watch:

"{\n    \"query\": {\n        \"size\": 0,\n ...."

• JSON.parse(param) throws error
• JSON.parse(JSON.stringify(param)) return success
• But JSON.parse(JSON.stringify('junk')) also returns success although a single word of junk is not considered valid json

So what kind of code routine would you recommend to handle this scenario? Is there some logic that I can use to format the sample input parameter value above, so that JSON.parse() will properly validate the param value as JSON?

Answer 1

I would use JSON.parse to validate JSON:

let valid = false;
try {
  JSON.parse(str);
  console.log('valid');
  valid = true;
} catch {
  console.log('invalid');
}
console.log(valid);

Examples:

const json = `{
    "query": {
        "size": 0,
        "aggregations": {
            "ipTag": {
                "terms": {
                    "field": "ipTag",
                    "size": 1001
                }
            }
        }
    },
    "table": "ip_info_table"
}`;

try {
    JSON.parse(json);
    console.log('valid');
} catch {
    console.log('invalid');
}

const json = "{\n    \"query\": {\n        \"size\": 0\n} }";

try {
    JSON.parse(json);
    console.log('valid');
} catch {
    console.log('invalid');
}

const json = `{
    "query": {
        "size": 0,
        "aggregations": {
            "ipTag": {
                "terms": {
                    "field": "ipTag",
                    "size": 1001
                }
            }
        }
    },
    "table": "ip_info_table",
}`;

try {
    JSON.parse(json);
    console.log('valid');
} catch {
    console.log('invalid');
}