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Tracker is a small library used for auto updating templates once the Session variable has changed. In this chapter, we will learn how the tracker works.
First, we will create a button that will be used for updating the session.
meteorApp.html
<head>
<title>meteorApp</title>
</head>
<body>
<div>
{{> myTemplate}}
</div>
</body>
<template name = "myTemplate">
<button id = "myButton">CLICK ME</button>
</template>
Next, we will set the starting session value myData and create a mySession object. Tracker.autorun method is used for keeping an eye on mySession. Whenever this object changes, the template will auto-update. To test it, we will set a click event for updating.
meteorApp.js
if (Meteor.isClient) {
var myData = 0
Session.set(''mySession'', myData);
Tracker.autorun(function () {
var sessionData = Session.get(''mySession'');
console.log(sessionData)
});
Template.myTemplate.events({
''click #myButton'': function() {
Session.set(''mySession'', myData ++);
}
});
}
If we click the CLICK ME button five times, we will see that the tracker is logging new values every time the session updates.
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