In many scenarios, the web application can only be started after the machine is connected to the network. If you are not connected to the Internet, an error will be prompted. ,
But sometimes the machine needs to be restarted. If the web application is started immediately after the machine restarts, the network service on the machine may not be ready.
Especially Windows 7, it takes several seconds to start the network service. What should I do at this time?
I've tried several methods before:
For example, it is judged by ping, but ping needs to have a non-native IP address. This is not very common
For example, monitoring whether a port has been occupied, but the optical port is occupied, it does not mean that the network has been started.
On the other hand, if it is a web application, it is best to make a judgment on the front end, such as using javascript.
Some people also write the simulation effect of ping on javascript. But it is indeed a bit troublesome.
What to do? At the critical moment, html5 can give a good solution:
Method 1:
if ()
{ //Work normally}
else { //Execute tasks when offline}
This new feature of html5's navigator can help us solve it very easily
HTML5 defines a property for this. The value of this property is true to indicate that the device can access the Internet, and a value of false to indicate that the device is offline.
Of course, different browsers support this is not the same
IE6+ and Safari 5+ support are better
Firefox 3+ and support properties, but you have to manually select the menu item "File-Web Developer (Settings)-Work Offline" to make the browser work properly.
Chrome requires more than 12.
Method 2:
Of course, if you want to support more compatible, you can use the following 2 events: online and offline. These two events are triggered separately when the network changes from offline to online or from online to offline. These two events are fired on the window object.
To detect whether the application is offline, it is best to get the initial state first after the page is loaded. Then, the above two events are used to determine whether the network connection status has changed. When the above event triggers, the value of the attribute will also change, but this attribute must be manually polled to detect changes in the network state.
var EventUtil = {
addHandler: function (element, type, handler) {
if () {
(type, handler, false);
} else if () {
("on" + type, handler);
} else {
element["on" + type] = handler;
}
}
};
(window, "online", function () {
alert("Online");
});
(window, "offline", function () {
alert("Offline");
});
But sometimes the machine needs to be restarted. If the web application is started immediately after the machine restarts, the network service on the machine may not be ready.
Especially Windows 7, it takes several seconds to start the network service. What should I do at this time?
I've tried several methods before:
For example, it is judged by ping, but ping needs to have a non-native IP address. This is not very common
For example, monitoring whether a port has been occupied, but the optical port is occupied, it does not mean that the network has been started.
On the other hand, if it is a web application, it is best to make a judgment on the front end, such as using javascript.
Some people also write the simulation effect of ping on javascript. But it is indeed a bit troublesome.
What to do? At the critical moment, html5 can give a good solution:
Method 1:
Copy the codeThe code is as follows:
if ()
{ //Work normally}
else { //Execute tasks when offline}
This new feature of html5's navigator can help us solve it very easily
HTML5 defines a property for this. The value of this property is true to indicate that the device can access the Internet, and a value of false to indicate that the device is offline.
Of course, different browsers support this is not the same
IE6+ and Safari 5+ support are better
Firefox 3+ and support properties, but you have to manually select the menu item "File-Web Developer (Settings)-Work Offline" to make the browser work properly.
Chrome requires more than 12.
Method 2:
Of course, if you want to support more compatible, you can use the following 2 events: online and offline. These two events are triggered separately when the network changes from offline to online or from online to offline. These two events are fired on the window object.
To detect whether the application is offline, it is best to get the initial state first after the page is loaded. Then, the above two events are used to determine whether the network connection status has changed. When the above event triggers, the value of the attribute will also change, but this attribute must be manually polled to detect changes in the network state.
Copy the codeThe code is as follows:
var EventUtil = {
addHandler: function (element, type, handler) {
if () {
(type, handler, false);
} else if () {
("on" + type, handler);
} else {
element["on" + type] = handler;
}
}
};
(window, "online", function () {
alert("Online");
});
(window, "offline", function () {
alert("Offline");
});