Remove a line from JSON parse

I am working with JIVE JSON RESTFul API and on their API they have a security

(I am referring to the throw 'allowIllegalResourceCall is false.'; )

throw 'allowIllegalResourceCall is false.';
{
  "id" : "52104", 
}

I am using this code to try to PARSE IT:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {   
        var myObj = JSON.parse(this.responseText);
        document.getElementById("topdisplay").innerHTML = myObj.id;
    }    
};
xmlhttp.open("GET", "http://mysite/API/",true);
xmlhttp.send();

And I am getting an error because of that starting line. I looked everywhere to try finding a solution to skip that to the JSON PARSE would work but I can't seem to find a way that works to do it.

Also I know that the parsing code works because when I remove the first line it works perfectly.

Any help?

JIVE REST API introduced this to help prevent against JSON Hijacking back when web browsers were susceptible.

You'll need to first find {, and do a substring from that position to the end of the string.

var xmlhttp = new XMLHttpRequest();

xmlhttp.onreadystatechange = function() {

    if (this.readyState == 4 && this.status == 200) {   
        var response = this.responseText
                var myObj = JSON.parse(this.responseText.substring(this.response.indexOf('{')));

        document.getElementById("topdisplay").innerHTML = myObj.id;
    }    
};

xmlhttp.open("GET", "http://mysite/API/",true);
xmlhttp.send();

NOTE:

using RegEx, you'll need to find the first line with throw and ending in a semi-colon, if found replace with an empty string.

JSON.parse(response.replace(/throw.*;/, "").trim());