I want to开发者_开发知识库 check when someone tries to refresh a page.

For example, when I open a page nothing happens but when I refresh the page it should display an alert.

⚠️⚠️⚠️ window.performance.navigation.type is deprecated. Please see Илья Зеленько's answer.

A better way to know that the page is actually reloaded is to use the navigator object that is supported by most modern browsers.

It uses the Navigation Timing API.

//check for Navigation Timing API support
if (window.performance) {
  console.info("window.performance works fine on this browser");
}
console.info(performance.navigation.type);
if (performance.navigation.type == performance.navigation.TYPE_RELOAD) {
  console.info( "This page is reloaded" );
} else {
  console.info( "This page is not reloaded");
}

Source: Navigation Timing API

New standard 2018-now (PerformanceNavigationTiming)

window.performance.navigation property is deprecated in the Navigation Timing Level 2 specification. Please use the PerformanceNavigationTiming interface instead.

PerformanceNavigationTiming.type

This is an experimental technology.

Check the Browser compatibility table carefully before using this in production.

Check if page gets reloaded or refreshed in JavaScript

const pageAccessedByReload = (
  (window.performance.navigation && window.performance.navigation.type === 1) ||
    window.performance
      .getEntriesByType('navigation')
      .map((nav) => nav.type)
      .includes('reload')
);

alert(pageAccessedByReload);

Support on 2021-11-09

Check if page gets reloaded or refreshed in JavaScript

The type read-only property returns a string representing the type of navigation. The value must be one of the following:

navigate — Navigation started by clicking a link, entering the URL in the browser's address bar, form submission, or initializing through a script operation other than reload and back_forward as listed below.
reload — Navigation is through the browser's reload operation or location.reload().
back_forward — Navigation is through the browser's history traversal operation.
prerender — Navigation is initiated by a prerender hint.

This property is Read only.

The following example illustrates this property's usage.

function print_nav_timing_data() {
  // Use getEntriesByType() to just get the "navigation" events
  var perfEntries = performance.getEntriesByType("navigation");

  for (var i=0; i < perfEntries.length; i++) {
    console.log("= Navigation entry[" + i + "]");
    var p = perfEntries[i];
    // dom Properties
    console.log("DOM content loaded = " + (p.domContentLoadedEventEnd - p.domContentLoadedEventStart));
    console.log("DOM complete = " + p.domComplete);
    console.log("DOM interactive = " + p.interactive);
 
    // document load and unload time
    console.log("document load = " + (p.loadEventEnd - p.loadEventStart));
    console.log("document unload = " + (p.unloadEventEnd - p.unloadEventStart));
    
    // other properties
    console.log("type = " + p.type);
    console.log("redirectCount = " + p.redirectCount);
  }
}

First step is to check sessionStorage for some pre-defined value and if it exists alert user:

if (sessionStorage.getItem("is_reloaded")) alert('Reloaded!');

Second step is to set sessionStorage to some value (for example true):

sessionStorage.setItem("is_reloaded", true);

Session values kept until page is closed so it will work only if page reloaded in a new tab with the site. You can also keep reload count the same way.

Store a cookie the first time someone visits the page. On refresh check if your cookie exists and if it does, alert.

function checkFirstVisit() {
  if(document.cookie.indexOf('mycookie')==-1) {
    // The cookie doesn't exist. Create it now
    document.cookie = 'mycookie=1';
  }
  else {
    // Not the first visit, so alert
    alert('You refreshed!');
  }
}

And in your body tag:

<body onload="checkFirstVisit()">

I have wrote this function to check both methods using old window.performance.navigation and new performance.getEntriesByType("navigation") in same time:

function navigationType(){

    var result;
    var p;

    if (window.performance.navigation) {
        result=window.performance.navigation;
        if (result==255){result=4} // 4 is my invention!
    }

    if (window.performance.getEntriesByType("navigation")){
       p=window.performance.getEntriesByType("navigation")[0].type;

       if (p=='navigate'){result=0}
       if (p=='reload'){result=1}
       if (p=='back_forward'){result=2}
       if (p=='prerender'){result=3} //3 is my invention!
    }
    return result;
}

Result description:

0: clicking a link, Entering the URL in the browser's address bar, form submission, Clicking bookmark, initializing through a script operation.

1: Clicking the Reload button or using Location.reload()

2: Working with browswer history (Bakc and Forward).

3: prerendering activity like <link rel="prerender" href="//example.com/next-page.html">

4: any other method.

event.currentTarget.performance.navigation.type

returns

0 => user just typed in an Url
1 => page reloaded
2 => back button clicked.

I found some information in JavaScript Detecting Page Refresh. His first recommendation is using hidden fields, which tend to be stored through page refreshes.

function checkRefresh() {
    if (document.refreshForm.visited.value == "") {
        // This is a fresh page load
        document.refreshForm.visited.value = "1";
        // You may want to add code here special for
        // fresh page loads
    } else {
        // This is a page refresh
        // Insert code here representing what to do on
        // a refresh
    }
}

<html>

<body onLoad="JavaScript:checkRefresh();">
    <form name="refreshForm">
        <input type="hidden" name="visited" value="" />
    </form>

</body>

</html>

Here is a method that is supported by nearly all browsers:

if (sessionStorage.getItem('reloaded') != null) {
    console.log('page was reloaded');
} else {
    console.log('page was not reloaded');
}

sessionStorage.setItem('reloaded', 'yes'); // could be anything

It uses SessionStorage to check if the page is opened the first time or if it is refreshed.

This implementation helped me:

From MDN reference 2022: Navigation Timing Level 2 specification

const navigationType = 
    (window.performance.getEntriesByType('navigation')
        [0] as PerformanceNavigationTiming).type;

const isPageReload = navigationType === 'reload';
const isNavigation = navigationType === 'navigate';
const isBackForwarad = navigationType === 'back_forward';
const isPrerender = navigationType === 'prerender';

if(sessionStorage.reload) { 
   sessionStorage.reload = true;
   // optionnal
   setTimeout( () => { sessionStorage.setItem('reload', false) }, 2000);
} else {
   sessionStorage.setItem('reload', false);
}

One easy solution has not been mentioned (not relying on the deprecated window.performance.navigation):

Use window.onbeforeunload to store the time and the URL of your current page (in localstorage) when the user leaves the page (potentially refreshes the page).

window.onbeforeunload = function(e)
{
    localStorage.setItem('reload-url', window.location.href);
}

Then use window.onload to get those values from localstorage.

window.onload = function(e)
{
    if (localStorage.getItem('reload-url') != null)) 
    {
        if (window.location.href == localStorage.getItem('reload-url'))
        {
            console.log('Reload');
        }
    }
}

If the recent URL matches the stored URL and if the stored time matches the current time (maybe with a tiny offset) then it is a page reload by the user.

Append the below Script in Console:

window.addEventListener("beforeunload", function(event) { 
     console.log("The page is redirecting")           
     debugger; 
});

<script>
    
    var currpage    = window.location.href;
    var lasturl     = sessionStorage.getItem("last_url");

    if(lasturl == null || lasturl.length === 0 || currpage !== lasturl ){
        sessionStorage.setItem("last_url", currpage);
        alert("New page loaded");
    }else{
        alert("Refreshed Page");  
    }

</script>

 document.addEventListener("keydown", (e)=>{
   if (e.keyCode === 116) {
     e.preventDefault();

      // your code here
      // var r = confirm("Reload!");
      // if (r == true)
      //  window.location.reload();
   }
 })

Here we used event listener 'keydown' because F1 - F12 keys are not available on browsers for 'keypress'.
116 is the keycode for 'F5'. Check here
'preventDefault()' will stop the default function of the key pressed. Here it stops direct refresh when F5 is pressed.
Then add your code.
When the alert is confirmed, 'location.reload()' will reload the page