Check if a string is a valid JSON

function isJson(str) {
    try {
        JSON.parse(str);
    } catch (e) {
      //the json is  not ok
        return false;
    }
    //the json is ok
    return true;									
}

Source

https://github.com/roeib/JavaScript-snippets#check-if-a-string-is-a-valid-json