Sending request from browser to ESP8266WebServer fails

Question

I have a server in my ESP8266-01. The ESP8266 is in softAP mode. ESP8266WebServer.h is used to create the server.

When I type 192.168.4.1/1/ in the browser, it returns a UI containing buttons. The buttons are generated from the following code:

addToBuffer("<div class=\"row\">");
for(i=1; i<5; i++) {
    addToBuffer("<div class=\"col-md-2\"><button class=\"btn btn-block btn-lg btn-primary\" id='btn_on");
    addToBuffer(clientId);
    addToBuffer(i);
    if(i==1)
        addToBuffer("'>UP</button></div>");
    if(i==2)
        addToBuffer("'>LEFT</button></div>");
    if(i==3)
        addToBuffer("'>RIGHT</button></div>");
    if(i==4)
        addToBuffer("'>DOWN</button></div>");
}
addToBuffer("</div>");

// JavaScript for buttons
addToBuffer("<script type='javascript'>");
for(i=1; i<5; i++) {
    addToBuffer("$('#btn_on");
    addToBuffer(clientId);
    addToBuffer(i);
    addToBuffer("').click(function(){var xmlHttp = new XMLHttpRequest();xmlHttp.open(\"GET\",'/");
    addToBuffer(clientId);
    addToBuffer("/");
    addToBuffer(i);
    addToBuffer("/',false);});");
    addToBuffer("xmlHttp.send(null);");
}
addToBuffer("</script>");

The server has handler functions for urls / /1, /1/1/ /1/2/ /1/3/ /1/4/.

When I press any of the buttons, no request is being received in server. How to solve this?