如何防止setInterval函数在Javascript中执行两次？
[英]How to prevent setInterval function from executing twice in Javascript?
问题描述
I am making JS Ajax call to update the contents of a page every 2 seconds. 
我正在进行JS Ajax调用，每2秒更新一次页面的内容。 To do this I am using setInterval method. 为此，我正在使用setInterval方法。 I have noticed that my setInterval method executed twice and as a result i get duplicate output. 我注意到我的setInterval方法执行了两次，结果得到重复的输出。 Check the images for reference. 检查图像以供参考。
My Flask backend - routes.py 我的Flask后端routes.py
@app.route('/image/<im>')
@login_required
def image(im):
image_src=[im+'/'+i for i in os.listdir(os.path.join(app.static_folder,im))]
rows=math.ceil(len(image_src)/3)
print(image_src)
return render_template('dashboard.html',title='Welcome',images=image_src,rows=rows,image_date=im)
My HTML - dashboard.html 我的HTML dashboard.html
{% extends "base.html" %}
{% block content %}
<div class="image-area">
<div class="container dash-container main-body" >
<hr>
<div class="row">
<br>
<hr >
<br>
<div class="col-md-12">
<div class="jumbotron ">
<h1 id="hdr">DASHBOARD</h1>
</div>
</div>
</div>
{% if images %}
<div class="row" id="info">
<a href="{{ url_for('dashboard') }}"><span class="glyphicon glyphicon-backward" aria-hidden="true"></span></a>
</div>
<br><br>
<div class="row">
<div class="col-md-12" id="info">
{% set ns = namespace(counter=0) %}
<table class="table table-hover table-condensed table-bordered images-table" cellspacing="5" cellpadding="5">
{% for row in range(rows) %}
<tr class="image-hover">
{% for data in range(3) %}
{% if ns.counter < images|length %}
<td style="width:10%;">
<a href="{{ url_for('display',file=images[ns.counter][10:],folder=images[ns.counter][0:10]) }}"><img src="{{ url_for('static',filename=images[ns.counter]) }}" alt="User Image" width="200" height="180"></a>
<br>
{% set ns.counter = ns.counter + 1 %}
</td>
{% endif %}
{% endfor %}
</tr>
{% endfor %}
</table>
</div>
</div>
{% endif %}
</div>
</div>
<script type="text/javascript">
var first_time = 0;
var current_count = 0;
var total_count = 0;
function update(){
if (window.first_time == 0){
window.current_count = $('td').length;
window.total_count = window.current_count;
window.first_time = 1;
//var txt = $("<p class='notify'></p>").text("No new images");
$('body').append("<p class='notify'>No new images</p>");
}
else {
window.total_count = $('td').length;
if (window.total_count>window.current_count){
$('.notify').text(window.total_count-window.current_count + " images added !");
$('html, body').animate({scrollTop:$(document).height()}, 'slow');
//window.alert(total_count-current_count + ' images added !');
window.current_count = window.total_count;
}
}
}
setInterval(function(){ $('.image-area').load("{{ url_for('image',im=image_date) }}"); update(); }, 2000);
</script>
{% endblock %}
base.HTML - base.HTML
<!DOCTYPE html>
<html>
<head>
{{ moment.include_jquery() }}
{{ moment.include_moment() }}
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/base.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/about.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/index.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/dashboard.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/display.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/feedback.css') }}">
<link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='styles/login.css') }}">
<link href="https://fonts.googleapis.com/css?family=Saira" rel="stylesheet">
{% if title %}
<title>{{ title }}</title>
{% else %}
<title>Welcome_segregator</title>
{% endif %}
</head>
<body>
<nav class="navbar navbar-fixed-top navbar-custom">
<div class="container" >
<div class="navbar-header">
{% if current_user.username %}
<a class="navbar-brand nav-custom" href="{{ url_for('index') }}" ><span id="header"><span id="logo"><strong>Welcome </strong></span id="header"><strong>{{ current_user.username|striptags }} !</strong></span></a>
{% else %}
<a class="navbar-brand nav-custom" href="{{ url_for('index') }}"><span id="header"><span id="logo"><strong>Welcome </strong></span></span></a>
{% endif %}
</div>
<ul class="nav navbar-nav navbar-right " >
<li class="nav-custom"><a class="nav navbar-nav" href="{{ url_for('index') }}"><span class="glyphicon glyphicon-home "> <span id="header"><strong>Home</strong></span></a></li>
<li><a class="nav navbar-nav" href="{{ url_for('dashboard') }}"><span class="glyphicon glyphicon-dashboard"> <span id="header"><strong>Dashboard</strong></span></a></li>
<li><a class="nav navbar-nav" href="{{ url_for('about') }}"><span class="glyphicon glyphicon-user"> <span id="header"><strong>About Us</strong></span></a></li>
<li><a class="nav navbar-nav" href="{{ url_for('feedback') }}"><span class="glyphicon glyphicon-pencil"> <span id="header"><strong>Feedback</strong></span></a></li>
{% if current_user.is_anonymous %}
<li><a class="nav navbar-nav" href="{{ url_for('login') }}"><span class="glyphicon glyphicon-log-in"> <span id="header"><strong>Login</strong></span></a></li>
{% else %}
<li><a class="nav navbar-nav" href="{{ url_for('logout') }}"><span class="glyphicon glyphicon-off"> <span id="header"><strong>Logout</strong></span></a></li>
{% endif %}
</ul>
</div>
</nav>
{% with messages = get_flashed_messages() %}
{% if messages %}
<ul>
{% for message in messages %}
<li>{{ message }}</li>
{% endfor %}
</ul>
{% endif %}
{% endwith %}
{% block content %}{% endblock %}
</body>
</html>
The setInterval method updates the page every 2 seconds and then calls the update() function. setInterval方法每2秒更新一次页面，然后调用update()函数。 update function implements a custom notification at the end of the HTML file which notifies the user if there is any new item. update函数在HTML文件的末尾实现自定义通知，该通知会通知用户是否有任何新项目。 As you can see in Image 1 and 2 , the notifications are being delivered twice on the page. 如您在图像1和2中所看到的，该通知在页面上发送了两次。
IMPORTANT :- The duplicate values are not being added immediately. 重要说明：-不会立即添加重复的值。 For the case when there is no new image, the message "No new images" is added after 2 seconds ie there is a gap of 2 seconds between the display of duplicate "No new images". 对于没有新图像的情况，消息“没有新图像”会在2秒后添加，即，显示重复的“没有新图像”之间会有2秒的间隔。 However, when there is a new image , then instead of the duplicates arriving 2 seconds later, they get added at the same time. 但是，当有新图像时，不是在2秒钟后到达副本，而是在同一时间添加它们。 ie the message "5 images added" and its duplicate version arrive at the screen at the same time. 即消息“已添加5张图像”及其重复版本会同时到达屏幕。
Notice the duplicate message updated at the bottom. 请注意，重复消息已在底部更新。
Notice the duplicates at the bottom. 请注意底部的重复项。 Here 5 new images were added to the dashboard and so notification is 5 which is correct but the display is duplicated. 在这里，向仪表板添加了5张新图像，因此通知为5，这是正确的，但是显示重复。
I want the notifications to be displayed only once. 我希望通知仅显示一次。 Please help. 请帮忙。
EDIT 1: - Here is the complete rendered HTML 编辑1： -这是完整的呈现的HTML
<!DOCTYPE html>
<html>
<head>
<script src="//code.jquery.com/jquery-2.1.0.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment-with-locales.min.js"></script>
<script>
moment.locale("en");
function flask_moment_render(elem) {
$(elem).text(eval('moment("' + $(elem).data('timestamp') + '").' + $(elem).data('format') + ';'));
$(elem).removeClass('flask-moment').show();
}
function flask_moment_render_all() {
$('.flask-moment').each(function() {
flask_moment_render(this);
if ($(this).data('refresh')) {
(function(elem, interval) { setInterval(function() { flask_moment_render(elem) }, interval); })(this, $(this).data('refresh'));
}
})
}
$(document).ready(function() {
flask_moment_render_all();
});
</script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<link rel="stylesheet" type="text/css" href="/static/styles/base.css">
<link rel="stylesheet" type="text/css" href="/static/styles/about.css">
<link rel="stylesheet" type="text/css" href="/static/styles/index.css">
<link rel="stylesheet" type="text/css" href="/static/styles/dashboard.css">
<link rel="stylesheet" type="text/css" href="/static/styles/display.css">
<link rel="stylesheet" type="text/css" href="/static/styles/feedback.css">
<link rel="stylesheet" type="text/css" href="/static/styles/login.css">
<link href="https://fonts.googleapis.com/css?family=Saira" rel="stylesheet">
<title>Welcome</title>
</head>
<body>
<nav class="navbar navbar-fixed-top navbar-custom">
<div class="container" >
<div class="navbar-header">
<a class="navbar-brand nav-custom" href="/index" ><span id="header"><span id="logo"><strong>Welcome </strong></span id="header"><strong>dev !</strong></span></a>
</div>
<ul class="nav navbar-nav navbar-right " >
<li class="nav-custom"><a class="nav navbar-nav" href="/index"><span class="glyphicon glyphicon-home "> <span id="header"><strong>Home</strong></span></a></li>
<li><a class="nav navbar-nav" href="/dashboard"><span class="glyphicon glyphicon-dashboard"> <span id="header"><strong>Dashboard</strong></span></a></li>
<li><a class="nav navbar-nav" href="/about"><span class="glyphicon glyphicon-user"> <span id="header"><strong>About Us</strong></span></a></li>
<li><a class="nav navbar-nav" href="/feedback"><span class="glyphicon glyphicon-pencil"> <span id="header"><strong>Feedback</strong></span></a></li>
<li><a class="nav navbar-nav" href="/logout"><span class="glyphicon glyphicon-off"> <span id="header"><strong>Logout</strong></span></a></li>
</ul>
</div>
</nav>
<div class="image-area">
<div class="container dash-container main-body" >
<hr>
<div class="row">
<br>
<hr >
<br>
<div class="col-md-12">
<div class="jumbotron ">
<h1 id="hdr">DASHBOARD</h1>
</div>
</div>
</div>
<div class="row" id="info">
<a href="/dashboard"><span class="glyphicon glyphicon-backward" aria-hidden="true"></span></a>
</div>
<br><br>
<div class="row">
<div class="col-md-12" id="info">
<table class="table table-hover table-condensed table-bordered images-table" cellspacing="5" cellpadding="5">
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-18-39+PM_0.9997674822807312_0.0002324927772860974_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-18-39%20PM_0.9997674822807312_0.0002324927772860974_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-19-26+PM_0.0011277222074568272_0.9988722205162048_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-19-26%20PM_0.0011277222074568272_0.9988722205162048_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-19-47+PM_0.9632670283317566_0.03673300892114639_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-19-47%20PM_0.9632670283317566_0.03673300892114639_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-20-31+PM_0.7819413542747498_0.21805864572525024_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-20-31%20PM_0.7819413542747498_0.21805864572525024_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-20-53+PM_0.03425532579421997_0.96574467420578_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-20-53%20PM_0.03425532579421997_0.96574467420578_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-23-59+PM_6.910012757543882e-07_0.9999992847442627_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-23-59%20PM_6.910012757543882e-07_0.9999992847442627_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_02-24-21+PM_0.0027463394217193127_0.9972537159919739_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_02-24-21%20PM_0.0027463394217193127_0.9972537159919739_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_03-27-32+PM_0.8725430369377136_0.1274568885564804_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_03-27-32%20PM_0.8725430369377136_0.1274568885564804_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-23-40+PM_0.9983899593353271_0.0016100991051644087_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-23-40%20PM_0.9983899593353271_0.0016100991051644087_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-24-43+PM_0.014673426747322083_0.9853265285491943_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-24-43%20PM_0.014673426747322083_0.9853265285491943_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-25-37+PM_0.028937892988324165_0.9710620641708374_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-25-37%20PM_0.028937892988324165_0.9710620641708374_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-26-08+PM_0.10836496949195862_0.8916350603103638_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-26-08%20PM_0.10836496949195862_0.8916350603103638_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-26-56+PM_0.9980469942092896_0.0019529901910573244_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-26-56%20PM_0.9980469942092896_0.0019529901910573244_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-27-32+PM_0.0008696855511516333_0.9991303086280823_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-27-32%20PM_0.0008696855511516333_0.9991303086280823_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-28-29+PM_0.9541159868240356_0.04588397219777107_bio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-28-29%20PM_0.9541159868240356_0.04588397219777107_bio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
<tr class="image-hover">
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-29-03+PM_0.0024711675941944122_0.9975288510322571_nonbio_.jpeg"><img src="/static/07-05-2018/07-05-18_04-29-03%20PM_0.0024711675941944122_0.9975288510322571_nonbio_.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
<td style="width:10%;">
<a href="/display?folder=07-05-2018&file=%2F07-05-18_04-29-25+PM_0.033340130001306534_0.9666599035263062_nonbio_+-+Copy+-+Copy+-+Copy+-+Copy+-+Copy+%282%29+-+Copy+-+Copy+-+Copy+-+Copy+-+Copy.jpeg"><img src="/static/07-05-2018/07-05-18_04-29-25%20PM_0.033340130001306534_0.9666599035263062_nonbio_%20-%20Copy%20-%20Copy%20-%20Copy%20-%20Copy%20-%20Copy%20%282%29%20-%20Copy%20-%20Copy%20-%20Copy%20-%20Copy%20-%20Copy.jpeg" alt="User Image" width="200" height="180"></a>
<br>
</td>
</tr>
</table>
</div>
</div>
</div>
</div>
<script type="text/javascript">
var first_time = 0;
var current_count = 0;
var total_count = 0;
function update(){
if (window.first_time == 0){
window.current_count = $('td').length;
window.total_count = window.current_count;
window.first_time = 1;
//var txt = $("<p class='notify'></p>").text("No new images");
$('body').append("<p class='notify'>No new images</p>");
}
else {
window.total_count = $('td').length;
if (window.total_count>window.current_count){
$('.notify').text(window.total_count-window.current_count + " images added !");
$('html, body').animate({scrollTop:$(document).height()}, 'slow');
//window.alert(total_count-current_count + ' images added !');
window.current_count = window.total_count;
}
}
}
setInterval(function(){ $('.image-area').load("/image/07-05-2018"); update(); }, 2000);
</script>
</body>
</html>
3 个解决方案
解决方案1
2 2018-05-11 06:40:58
Take your set interval function in a variable and simply pass that variable into clearInterval() function your interval function execute once only 将您设置的间隔函数放入变量中，然后将该变量简单地传递给clearInterval（）函数，间隔函数仅执行一次
var myVar = setInterval(function(){ myTimer() }, 2000);
function myTimer() {
$('.image-area').load("{{ url_for('image',im=image_date) }}");
update();
}
setInterval(function(){
clearInterval(myVar);
}, 2000);
解决方案2
2 已采纳 2018-05-11 07:20:25
I checked your javascript and you are using global window variables that dont exist instead of the local variables you predefined.
我检查了您的JavaScript，发现您使用的是不存在的全局窗口变量，而不是您预定义的局部变量。
Firstly I think you should use the local variables you defined. 首先，我认为您应该使用定义的局部变量。
var first_time = 0;
var current_count = 0;
var total_count = 0;
function update(){
if (first_time === 0){
current_count = $('td').length;
total_count = current_count;
first_time = 1;
//var txt = $("<p class='notify'></p>").text("No new images");
$('body').append("<p class='notify'>No new images</p>");
}
else {
total_count = $('td').length;
if (total_count>current_count){
$('.notify').text(total_count-current_count + " images added !");
$('html, body').animate({scrollTop:$(document).height()}, 'slow');
//alert(total_count-current_count + ' images added !');
current_count = total_count;
}
}
}
I hope this helps. 我希望这有帮助。
I'll like you to try using a callback function at the end of the image load since its likely the update function might be called twice because the image load might be taking longer than 2 seconds to load its resource thereby causing setInterval to catch up with it. 我希望您在图像加载结束时尝试使用回调函数，因为它可能会两次调用update函数，因为图像加载可能需要2秒钟以上的时间来加载其资源，从而导致setInterval赶上它。
setInterval(function(){
$('.image-area').load("{{ url_for('image',im=image_date) }}", function() {
update();
});
}, 2000);
解决方案3
0 2018-05-11 07:31:57
var myVar = setInterval(function(){ myTimer() }, 2000);
function myTimer() {
$('.image-area').load("{{ url_for('image',im=image_date) }}");
update();
}
setInterval(function(){
clearInterval(myVar);
}, 2000);
try this :) 尝试这个 ：）
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