AJAX: Check if a string is JSON?

Question

My JavaScript sometimes crashes on this line:

var json = eval(\'(\' + this.responseText + \')\');

Crashes are caused when the argument of <

Answer 1

The problem with depending on the try-catch approach is that JSON.parse('123') = 123 and it will not throw an exception. Therefore, In addition to the try-catch, we need to check the type as follows:

function isJsonStr(str) {
    var parsedStr = str;
    try {
        parsedStr = JSON.parse(str);
    } catch (e) {
        return false;
    }
    return typeof parsedStr == 'object'
}