Check Internet connectivity with jquery

问题

I am trying to check for the internet connection by sending a GET request to the server. I am a beginner in jquery and javascript. I am not using navigator.onLine for my code as it works differently in different browsers. This is my code so far:

var check_connectivity={
        is_internet_connected : function(){
            var dfd = new $.Deferred();
            $.get("/app/check_connectivity/")
            .done(function(resp){
                return dfd.resolve();
            })
            .fail(function(resp){
                return dfd.reject(resp);
            })
            return dfd.promise();
        },
}

I call this code in different file as:

if(!this.internet_connected())
        {
            console.log("internet not connected");
            //Perform actions
        }
internet_connected : function(){
        return check_connectivity.is_internet_connected();
},

The is_internet_connected() function returns a deferred object whereas I just need an answer in true/false. Can anybody tell me about how to achieve this?

回答1:

$.get() returns a jqXHR object, which is promise compatible - therefore no need to create your own $.Deferred.

var check_connectivity = {
    ...
    is_internet_connected: function() {
        return $.get({
            url: "/app/check_connectivity/",
            dataType: 'text',
            cache: false
        });
    },
    ...
};

Then :

check_connectivity.is_internet_connected().done(function() {
    //The resource is accessible - you are **probably** online.
}).fail(function(jqXHR, textStatus, errorThrown) {
    //Something went wrong. Test textStatus/errorThrown to find out what. You may be offline.
});

As you can see, it's not possible to be definitive about whether you are online or offline. All javascript/jQuery knows is whether a resource was successfully accessed or not.

In general, it is more useful to know whether a resource was successfully accessed (and that the response was cool) than to know about your online status per se. Every ajax call can (and should) have its own .done() and .fail() branches, allowing appropriate action to be taken whatever the outcome of the request.

回答2:

100% Working:

function checkconnection() {
    var status = navigator.onLine;
    if (status) {
        alert('Internet connected !!');
    } else {
        alert('No internet Connection !!');
    }
}

回答3:

Do you mean to check the internet connection if it's connected?

If so, try this:

$.ajax({
    url: "url.php",
    timeout: 10000,
    error: function(jqXHR) { 
        if(jqXHR.status==0) {
            alert(" fail to connect, please check your connection settings");
        }
    },
    success: function() {
        alert(" your connection is alright!");
    }
});

回答4:

you cannot get simple true or false in return, give them a callback handler

function is_internet_connected(callbackhandler)
{
$.get({
  url: "/app/check_connectivity/",
  success: function(){
     callbackhandler(true);
  },
  error: function(){
     callbackhandler(false);
  },
  dataType: 'text'
});
}

回答5:

try this 
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script>
 if (! window.jQuery) {
 alert('No internet Connection !!');
  }
 else {
 // internet connected
 }

Jquery Plugin for Detecting Internet Connection

回答6:

I just use the navigator onLine property, according to W3C http://www.w3schools.com/jsref/prop_nav_online.asp

BUT navigator only tells us if the browser has internet capability (connected to router, 3G or such). So if this returns false you are probably offline but if it returns true you can still be offline if the network is down or really slow. This is the time to check for an XHR request.

setInterval(setOnlineStatus(navigator.onLine), 10000);

function setOnlineStatus(online)
{
    if (online) {
    //Check host reachable only if connected to Router/Wifi/3G...etc
        if (hostReachable())
            $('#onlineStatus').html('ONLINE').removeAttr('class').addClass('online');
        else
            $('#onlineStatus').html('OFFLINE').removeAttr('class').addClass('offline');
    } else {
        $('#onlineStatus').html('OFFLINE').removeAttr('class').addClass('offline');
    }
}

function hostReachable()
{
    // Handle IE and more capable browsers
    var xhr = new (window.ActiveXObject || XMLHttpRequest)("Microsoft.XMLHTTP");
    var status;

    // Open new request as a HEAD to the root hostname with a random param to bust the cache
    xhr.open("HEAD", "//" + window.location.hostname + "/?rand=" + Math.floor((1 + Math.random()) * 0x10000), false);

    // Issue request and handle response
    try {
        xhr.send();
        return (xhr.status >= 200 && (xhr.status < 300 || xhr.status === 304));
    } catch (error) {
        return false;
    }

}

EDIT: Use port number if it is different than 80, otherwise it fails.

xhr.open("HEAD", "//" + window.location.hostname + ":" + window.location.port + "/?rand=" + Math.floor((1 + Math.random()) * 0x10000), false);

来源：https://stackoverflow.com/questions/20043215/check-internet-connectivity-with-jquery