Question

I have the below code:

sendRequest : function(data){
                var me = this;
                this._createData(data);
                try{
                    this.req.open(this.method,this.page,true);
                    this.req.onreadystatechange=function()
                    {
                        if (this.readyState==4 && this.status==200)
                        {
                            if(this.responseText)
                                var response = eval('(' + this.responseText + ')');
                            else 
                                response = null;
                            me.callBack(response);
                            return false;
                        }
                    }
                    this.req.send(this.data);
                } catch(err){
                    me.callBack(response);
                }
            },

It works fine, and returns what I expect it to return, but when the connection is lost, it doesn’t go into the catch block. What I want to know is how catch the request when server page is not available.

Answer 1

Here’s an example from Microsoft’s doc page for onreadystatechange:

function reportStatus()
{
    if (oReq.readyState == 4 /* complete */) {
        if (oReq.status == 200 || oReq.status == 304) {
            alert('Transfer complete.');
        }
        else {
            // error occurred
        }
    }
}

var oReq = new XMLHttpRequest();
oReq.open("GET", "http://localhost/test.xml", true);
oReq.onreadystatechange = reportStatus;
oReq.send();

Look where it says // error occurred.

There is a similar code example on this MDN documentation page.