blocks|key|943540|text|还有另一种检查方法-检查推荐人。第一个页面通常会有一个空的引用...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|943541|if+(document.referrer+==+"")+{
++++window.close()
}+else+{
++++history.back()
}|code-block|syntax|javascript|943542|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>There is another way to check - check the referrer. The first page usually will have an empty referrer...</p>

<pre><code>if (document.referrer == "") {
    window.close()
} else {
    history.back()
}
</code></pre>


blocks|key|1157716|text|我的代码让浏览器返回一个页面，如果失败，它会加载一个后备url。它还可以检测hashtag更改。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1157717|当后退按钮不可用时，后退url将在500毫秒后加载，因此浏览器有足够的时间加载上一页。在window.history.go(-1);之后加载回退url会导致浏览器使用回退url，因为js脚本还没有停止。|offset|length|style|CODE|1157718|function+historyBackWFallback(fallbackUrl)+{
++++fallbackUrl+=+fallbackUrl+%7C%7C+'/';
++++var+prevPage+=+window.location.href;

++++window.history.go(-1);

++++setTimeout(function(){+
++++++++if+(window.location.href+==+prevPage)+{
++++++++++++window.location.href+=+fallbackUrl;+
++++++++}
++++},+500);
}|code-block|syntax|javascript|1157719|entityMap^0|0|18|M|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

<p>My code let the browser go back one page, and if that fails it loads a fallback url. It also detect hashtags changes.</p>

<p>When the back button wasn't available, the fallback url will be loaded after 500 ms, so the browser has time enough to load the previous page. Loading the fallback url right after <code>window.history.go(-1);</code> would cause the browser to use the fallback url, because the js script didn't stop yet.</p>

<pre><code>function historyBackWFallback(fallbackUrl) {
    fallbackUrl = fallbackUrl || '/';
    var prevPage = window.location.href;

    window.history.go(-1);

    setTimeout(function(){ 
        if (window.location.href == prevPage) {
            window.location.href = fallbackUrl; 
        }
    }, 500);
}
</code></pre>


blocks|key|943727|text|请小心使用window.history.length，因为它还包含window.history.forward()的条目|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|943728|因此，您可能有超过1个条目的window.history.length，但没有历史回溯条目。这意味着如果您触发window.history.back()，则不会发生任何事情|943729|entityMap^0|5|L|X|O|0|E|L|1J|L|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|I|$]]

<p>Be careful with <code>window.history.length</code> because it also includes entries for <code>window.history.forward()</code></p>
<p>So you may have maybe <code>window.history.length</code> with more than 1 entries, but no history back entries.
This means that nothing happens if you fire <code>window.history.back()</code></p>


blocks|key|943646|text|history.length是无用的，因为它不会显示用户是否可以返回历史。此外，不同的浏览器使用初始值0或1-这取决于浏览器。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|943647|可行的解决方案是使用$(window).on('beforeunload'事件，但如果页面通过ajax加载并使用pushState更改窗口历史记录，我不确定它是否有效。|943648|所以我使用了下一个解决方案：|943649|var+currentUrl+=+window.location.href;
window.history.back();
setTimeout(function(){
++++//+if+location+was+not+changed+in+100+ms,+then+there+is+no+history+back
++++if(currentUrl+===+window.location.href){
++++++++//+redirect+to+site+root
++++++++window.location.href+=+'/';
++++}
},+100);|code-block|syntax|javascript|943650|entityMap^0|0|E|0|A|R|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|W|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|X|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

<p><code>history.length</code> is useless as it does not show if user can go back in history.
Also different browsers uses initial values 0 or 1 - it depends on browser.</p>

<p>The working solution is to use <code>$(window).on('beforeunload'</code> event, but I'm not sure that it will work if page is loaded via ajax and uses pushState to change window history.</p>

<p>So I've used next solution:</p>

<pre><code>var currentUrl = window.location.href;
window.history.back();
setTimeout(function(){
    // if location was not changed in 100 ms, then there is no history back
    if(currentUrl === window.location.href){
        // redirect to site root
        window.location.href = '/';
    }
}, 100);
</code></pre>


blocks|key|944008|text|基于答案here和here。我认为，更有说服力的答案是检查这是否是新选项卡中的新页面。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|944009|如果页面的历史记录不止一个，那么我们可以返回到当前页面之前的页面。如果不是，则该选项卡是新打开的选项卡，我们需要创建一个新选项卡。|944010|不同的是，对于链接的答案，我们不会检查referrer，因为新选项卡仍将具有推荐人。|style|CODE|944011|if(1+<+history.length)+{
++++history.back();
}
else+{
++++window.close();
}|code-block|syntax|javascript|944012|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/47033098/1945948|1|https://stackoverflow.com/a/7651297/1945948^0|4|4|0|9|4|1|0|0|J|8|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]|$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|16|8|@$A|17|B|18|H|I]]|9|@]|C|$]]|$1|J|3|K|5|L|7|19|8|@]|9|@]|C|$M|N]]|$1|O|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]]]

<p>Building on the answer <a href="https://stackoverflow.com/a/47033098/1945948">here</a> and <a href="https://stackoverflow.com/a/7651297/1945948">here</a>. I think, the more conclusive answer is just to check if this is a new page in a new tab.</p>

<p>If the history of the page is more than one, then we can go back to the page previous to the current page. If not, the tab is a newly opened tab and we need to create a new tab.</p>

<p>Differently, to the answers linked, we are not checking for a <code>referrer</code> as a new tab will still have a referrer.</p>

<pre><code>if(1 &lt; history.length) {
    history.back();
}
else {
    window.close();
}
</code></pre>


blocks|key|943769|text|我想出了以下方法。它利用onbeforeunload事件来检测浏览器是否开始离开页面。如果在某个时间跨度内没有，它将重定向到回退。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|943770|var+goBack+=+function+goBack(fallback){
++++var+useFallback+=+true;

++++window.addEventListener("beforeunload",+function(){
++++++useFallback+=+false;
++++});

++++window.history.back();

++++setTimeout(function(){
++++++++if+(useFallback){+window.location.href+=+fallback;+}
++++},+100);+
}|code-block|syntax|javascript|943771|您可以使用goBack("fallback.example.org")调用此函数。|offset|length|style|CODE|943772|entityMap^0|0|0|5|U|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

<p>I came up with the following approach. It utilizes the onbeforeunload event to detect whether the browser starts leaving the page or not. If it does not in a certain timespan it'll just redirect to the fallback.</p>

<pre><code>var goBack = function goBack(fallback){
    var useFallback = true;

    window.addEventListener("beforeunload", function(){
      useFallback = false;
    });

    window.history.back();

    setTimeout(function(){
        if (useFallback){ window.location.href = fallback; }
    }, 100); 
}
</code></pre>

<p>You can call this function using <code>goBack("fallback.example.org")</code>.</p>


blocks|key|944252|text|这对我使用react是有效的，但在另一种情况下也可以；当历史记录在第一页时(您不能返回)，window.history.status将为空，所以如果您想知道是否可以返回，您只需要：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|944253|+if+(window.history.state+==+null)+{
++++//you+cannot+go+back
+}|code-block|syntax|javascript|944254|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>This work for me using react but can work in another case; when history is in the first page (you cannot go back) window.history.status will be null, so if you want to know if you can navigate back you only need:</p>
<pre><code> if (window.history.state == null) {
    //you cannot go back
 }
</code></pre>


blocks|key|1157925|text|浏览器有后退和前进按钮。关于这个问题，我想出了一个解决方案。但它会影响浏览器的转发操作，并在某些浏览器上造成bug。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1157926|它的工作原理是这样的:如果浏览器打开一个从未打开过的新url，history.length将会增长。|1157927|因此，您可以像这样更改散列|1157928|++location.href+=+'#__transfer__'+%2B+new+Date().getTime()+|code-block|syntax|javascript|1157929|为了得到一个从未显示过的url，那么history.length将得到真实的长度。|1157930|++var+realHistoryLength+=+history.length+-+1|1157931|但是，它并不总是工作得很好，我不知道为什么，特别是当url自动跳转得很快的时候。|1157932|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

<p>the browser has back and forward button. I come up a solution on this question. but It will affect browser forward action and cause bug with some browsers.</p>

<p>It works like that:  If the browser open a new url, that has never opened, the history.length will be grow. </p>

<p>so you can change hash like</p>

<pre><code>  location.href = '#__transfer__' + new Date().getTime() 
</code></pre>

<p>to get a never shown url, then history.length will get the true length.</p>

<pre><code>  var realHistoryLength = history.length - 1
</code></pre>

<p>but, It not always work well, and I don't known why ,especially the when url auto jump quickly.</p>


blocks|key|1158156|text|我试图找到一个解决方案，这是我能得到的最好的解决方案(但效果很好，这是我在这里找到的最简单的解决方案)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1158157|在我的例子中，我想使用back按钮返回历史，但如果用户打开的第一个页面是我的应用程序的一个子页面，它将返回到主页。|1158158|解决方案是，一旦加载了应用程序，我就替换了历史状态：|1158159|history.replaceState(+{root:+true},+'',+window.location.pathname+%2B+window.location.hash)|code-block|syntax|javascript|1158160|这样，我只需要在返回之前检查一下history.state.root。如果为true，我将替换一个历史记录：|offset|length|style|CODE|1158161|if(history.state+&&+history.state.root)
++++history.replaceState(+{root:+true},+'',+'/')
else
++++history.back()+|1158162|entityMap^0|0|0|0|0|G|I|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|Y|8|@$M|Z|N|10|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|H|7|11|8|@]|9|@]|A|$I|J]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

<p>I was trying to find a solution and this is the best i could get (but works great and it's the easiest solution i've found even here).</p>
<p>In my case, i wanted to go back on history with an back button, but if the first page the user opened was an subpage of my app, it would go back to the main page.</p>
<p>The solution was, as soon the app is loaded, i just did an replace on the history state:</p>
<pre class="lang-js prettyprint-override"><code>history.replaceState( {root: true}, '', window.location.pathname + window.location.hash)
</code></pre>
<p>This way, i just need to check <code>history.state.root</code> before go back. If true, i make an history replace instead:</p>
<pre class="lang-js prettyprint-override"><code>if(history.state &amp;&amp; history.state.root)
    history.replaceState( {root: true}, '', '/')
else
    history.back() 
</code></pre>


blocks|key|944127|text|我找到了一个实际有效的JQuery解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|944128|window.history.length+==+1|offset|length|style|CODE|944129|这适用于Chrome、Firefox和Edge。如果你想在没有窗口历史记录的情况下隐藏或删除你开发的网页上的后退按钮，你可以使用下面的JQuery代码，这段代码在上述三种浏览器的最新版本上都有效。|944130|$(window).load(function()+{
++++++++if+(window.history.length+==+1)+{
++++++++++++$("#back-button").remove();
++++++++}
++++})|code-block|syntax|javascript|944131|entityMap^0|0|0|Q|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|U|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|V|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

<h2>I found a JQuery solution that actually works</h2>
<p><code>window.history.length == 1</code></p>
<p>This works on Chrome, Firefox, and Edge.
You can use the following piece of JQuery code that worked for me on the latest versions of all of the above 3 browsers if you want to hide or remove a back button on your developed web page when there is no window history.</p>
<pre><code>$(window).load(function() {
        if (window.history.length == 1) {
            $(&quot;#back-button&quot;).remove();
        }
    })
</code></pre>


blocks|key|1158271|text|var+func+=+function(){+console.log("do+something");+};
if(document.referrer.includes(window.location.hostname)+&&+history.length-1+<=+1){
++++func();
}
else{
++++const+currentUrl+=+window.location.href;
++++history.back();
++++setTimeout(function(){
++++++++currentUrl+===+window.location.href+&&+func();
++++},+100);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1158272|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>var func = function(){ console.log(&quot;do something&quot;); };
if(document.referrer.includes(window.location.hostname) &amp;&amp; history.length-1 &lt;= 1){
    func();
}
else{
    const currentUrl = window.location.href;
    history.back();
    setTimeout(function(){
        currentUrl === window.location.href &amp;&amp; func();
    }, 100);
}
</code></pre>


blocks|key|943668|text|var+fallbackUrl+=+"home.php";
if(history.back()+===+undefined)
++++window.location.href+=+fallbackUrl;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|943669|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>var fallbackUrl = "home.php";
if(history.back() === undefined)
    window.location.href = fallbackUrl;
</code></pre>


blocks|key|1158264|text|我使用了一点PHP来达到这个效果。虽然有点生疏了。但它应该能行得通。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1158265|<?php+
function+pref(){+
++return+(isset($_SERVER['HTTP_REFERER']))+?+true+:+'';
}
?>
<html>
<body>

<input+type="hidden"+id="_pref"+value="<?=pref()?>">

<button+type="button"+id="myButton">GoBack</button>


<script>+
++if+(!$('#_pref').val())+{+
++++$('#myButton').hide()+//+or+$('#myButton').remove()
++}+
</script>
</body>
</html>|code-block|syntax|javascript|1158266|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>I am using a bit of PHP to achieve the result. It's a bit rusty though. But it should work.</p>
<pre><code>&lt;?php 
function pref(){ 
  return (isset($_SERVER['HTTP_REFERER'])) ? true : '';
}
?&gt;
&lt;html&gt;
&lt;body&gt;

&lt;input type=&quot;hidden&quot; id=&quot;_pref&quot; value=&quot;&lt;?=pref()?&gt;&quot;&gt;

&lt;button type=&quot;button&quot; id=&quot;myButton&quot;&gt;GoBack&lt;/button&gt;

&lt;!-- Include jquery library --&gt;
&lt;script&gt; 
  if (!$('#_pref').val()) { 
    $('#myButton').hide() // or $('#myButton').remove()
  } 
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>


blocks|key|943853|text|解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|943854|'use+strict';
function+previousPage()+{
++if+(window.location.pathname.split('/').filter(({+length+})+=>+length+>+0).length+>+0)+{
++++window.history.back();
++}
}|code-block|syntax|javascript|943855|解释|943856|window.location.pathname将为您提供当前URI。例如，https://domain/question/1234/i-have-a-problem将提供/question/1234/i-have-a-problem。有关更多信息，请参阅有关window.location的文档。|offset|length|style|CODE|943857|接下来，对split()的调用将为我们提供该URI的所有片段。因此，如果我们使用前面的URI，就会得到类似于["",+"question",+"1234",+"i-have-a-problem"]的东西。有关更多信息，请参阅有关String.prototype.split()的文档。|943858|这里调用filter()是为了过滤掉反斜杠生成的空字符串。它基本上只返回长度大于1的片段URI+(非空字符串)。所以我们会有像["question",+"1234",+"i-have-a-question"]这样的东西。这可以写成这样：|943859|'use+strict';
window.location.pathname.split('/').filter(function(fragment)+{
++return+fragment.length+>+0;
});|943860|有关更多信息，请参阅有关Array.prototype.filter()和Destructuring+assignment的文档。|943861|现在，如果用户在https://domain/上尝试返回，我们不会触发if+-语句，因此不会触发window.history.back()方法，因此用户将留在我们的网站上。这个URL等同于长度为0的[]，0+>+0为false。因此，默默地失败了。当然，如果您愿意，您可以记录一些内容或执行其他操作。|943862|'use+strict';
function+previousPage()+{
++if+(window.location.pathname.split('/').filter(({+length+})+=>+length+>+0).length+>+0)+{
++++window.history.back();
++}+else+{
++++alert('You+cannot+go+back+any+further...');
++}
}|943863|局限性|943864|当然，如果浏览器不支持History+API，这个解决方案将不起作用。在使用此解决方案之前，请查看文档以了解更多信息。|943865|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/API/Window/location|1|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split|2|https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/filter|3|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment|4|https://developer.mozilla.org/en-US/docs/Web/API/History_API^0|0|0|0|0|O|12|19|2E|V|3M|F|0|0|5|7|1I|18|36|O|1|0|4|8|1R|15|0|0|C|O|2|11|O|3|0|8|F|1C|L|2P|1|2R|2|2U|5|0|0|0|B|B|4|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1M|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1N|8|@$K|1O|L|1P|M|N]|$K|1Q|L|1R|M|N]|$K|1S|L|1T|M|N]]|9|@$K|1U|L|1V|1|1W]]|A|$]]|$1|O|3|P|5|6|7|1X|8|@$K|1Y|L|1Z|M|N]|$K|20|L|21|M|N]]|9|@$K|22|L|23|1|24]]|A|$]]|$1|Q|3|R|5|6|7|25|8|@$K|26|L|27|M|N]|$K|28|L|29|M|N]]|9|@]|A|$]]|$1|S|3|T|5|D|7|2A|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|2B|8|@]|9|@$K|2C|L|2D|1|2E]|$K|2F|L|2G|1|2H]]|A|$]]|$1|W|3|X|5|6|7|2I|8|@$K|2J|L|2K|M|N]|$K|2L|L|2M|M|N]|$K|2N|L|2O|M|N]|$K|2P|L|2Q|M|N]|$K|2R|L|2S|M|N]]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|2T|8|@]|9|@]|A|$E|F]]|$1|10|3|11|5|6|7|2U|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|2V|8|@]|9|@$K|2W|L|2X|1|2Y]]|A|$]]|$1|14|3|-4|5|6|7|2Z|8|@]|9|@]|A|$]]]|15|$16|$5|17|18|19|A|$1A|1B]]|1C|$5|17|18|19|A|$1A|1D]]|1E|$5|17|18|19|A|$1A|1F]]|1G|$5|17|18|19|A|$1A|1H]]|1I|$5|17|18|19|A|$1A|1J]]]]

<h2>Solution</h2>

<pre><code>'use strict';
function previousPage() {
  if (window.location.pathname.split('/').filter(({ length }) =&gt; length &gt; 0).length &gt; 0) {
    window.history.back();
  }
}
</code></pre>

<h2>Explaination</h2>

<p><code>window.location.pathname</code> will give you the current URI. For instance <code>https://domain/question/1234/i-have-a-problem</code> will give <code>/question/1234/i-have-a-problem</code>. See the documentation about <a href="https://developer.mozilla.org/en-US/docs/Web/API/Window/location" rel="nofollow noreferrer">window.location</a> for more informations.</p>

<p>Next, the call to <code>split()</code> will give us all fragments of that URI. so if we take our previous URI, we will have something like <code>["", "question", "1234", "i-have-a-problem"]</code>. See the documentation about <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split" rel="nofollow noreferrer">String.prototype.split()</a> for more informations.</p>

<p>The call to <code>filter()</code> is here to filter out the empty string generated by the backward slash. It will basically return only the fragment URI that have a length greater than 1 (non-empty string). So we would have something like <code>["question", "1234", "i-have-a-question"]</code>. This could have been writen like so:</p>

<pre><code>'use strict';
window.location.pathname.split('/').filter(function(fragment) {
  return fragment.length &gt; 0;
});
</code></pre>

<p>See the documentation about <a href="https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/filter" rel="nofollow noreferrer">Array.prototype.filter()</a> and the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment" rel="nofollow noreferrer">Destructuring assignment</a> for more informations.</p>

<p>Now, if the user tries to go back while being on <code>https://domain/</code>, we wont trigger the if-statement, and so wont trigger the <code>window.history.back()</code> method so the user will stay in our website. This URL will be equivalent to <code>[]</code> which has a length of <code>0</code>, and <code>0 &gt; 0</code> is false. Hence, silently failing. Of course, you can log something or have another action if you want.</p>

<pre><code>'use strict';
function previousPage() {
  if (window.location.pathname.split('/').filter(({ length }) =&gt; length &gt; 0).length &gt; 0) {
    window.history.back();
  } else {
    alert('You cannot go back any further...');
  }
}
</code></pre>

<h2>Limitations</h2>

<p>Of course, this solution wont work if the browser do not support the <a href="https://developer.mozilla.org/en-US/docs/Web/API/History_API" rel="nofollow noreferrer">History API</a>. Check the documentation to know more about it before using this solution.</p>


blocks|key|943488|text|我不确定这是否有效，而且它是完全未经测试的，但试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|943489|<script+type="text/javascript">

++++function+goBack()+{
++++++++history.back();
++++}

++++if+(history.length+>+0)+{+//if+there+is+a+history...
++++++++document.getElementsByTagName('button')[].onclick="goBack()";+//assign+function+"goBack()"+to+all+buttons+onClick
++++}+else+{
++++++++die();
++++}
</script>|code-block|syntax|javascript|943490|在HTML中的某个地方：|943491|<button+value="Button1">+//These+buttons+have+no+action
<button+value="Button2">|943492|编辑：|943493|您还可以做的是研究哪些浏览器支持back功能(我认为它们都支持)，并使用在this+page上找到并详细描述的标准JavaScript浏览器检测对象。然后你可以有两个不同的页面:一个是与后退按钮兼容的“好浏览器”，另一个是“坏浏览器”，告诉他们去更新他们的浏览器。|offset|length|943494|entityMap|0|LINK|mutability|MUTABLE|url|http://www.w3schools.com/js/js_browser.asp^0|0|0|0|0|0|11|9|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@$O|14|P|15|1|16]]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

<p>I'm not sure if this works and it is completely untested, but try this:</p>

<pre><code>&lt;script type="text/javascript"&gt;

    function goBack() {
        history.back();
    }

    if (history.length &gt; 0) { //if there is a history...
        document.getElementsByTagName('button')[].onclick="goBack()"; //assign function "goBack()" to all buttons onClick
    } else {
        die();
    }
&lt;/script&gt;
</code></pre>

<p>And somewhere in HTML:</p>

<pre><code>&lt;button value="Button1"&gt; //These buttons have no action
&lt;button value="Button2"&gt;
</code></pre>

<h2>EDIT:</h2>

<p>What you can also do is to research what browsers support the back function (I think they all do) and use the standard JavaScript browser detection object found, and described thoroughly, on <a href="http://www.w3schools.com/js/js_browser.asp" rel="nofollow noreferrer">this page</a>. Then you can have 2 different pages: one for the "good browsers" compatible with the back button and one for the "bad browsers" telling them to go update their browser</p>


blocks|key|1157657|text|检查window.history.length是否等于0。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1157658|entityMap^0|2|L|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

<p>Check if <code>window.history.length</code> is equal to 0.</p>


<p>I want using JavaScript to see if there is history or not, I mean if the back button is available on the browser or not.</p>


How to check if the user can go back in browser history or not

我想使用JavaScript查看是否有历史记录，我的意思是浏览器上的后退按钮是否可用。

问如何检查用户是否可以返回浏览器历史记录
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回答 16

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