CODEWITHSUNDEEP
javascriptmobilecordovaphonegap-plugins
Mumthezir VP
Mumthezir VP

Reputation: 6551

how to keep a variable in overall page scope - Javascript

Iam a new guy in JS and iam doing a mobile project in phonegap, i want to know how to keep a variable in overall page scope, not global variable since it will eat lot of memory which is not acceptable for a mobile developer, i have two or more JS tags in a page as shown,

<script type="text/javascript">
// script one here
</script>

<html> //html block here </html>

<script type="text/javascript">
// script two here
</script>

so i request your valuable suggestion & help. Thanks!

Upvotes: 0

Views: 1197

Answers (1)

Benjamin Gruenbaum
Benjamin Gruenbaum

Reputation: 276326

"Overall Page scope" is global scope.

JavaScript scoping (generally, except for specific esoteric scopes*) works in two ways:

  • Global scope
  • Closure scope (the scope created by a function)

Since you can't share a function over script tags, a global is your only choice.

Consider passing messages to share data instead of a global.

Here is how something like this could be done with message passing:

Script 0:

window.pubsub = (function(){
       var subscribers = [];
       return {
            subscribe:function(user){
                subscribers.push(user);
            },
            publish:function(message,data){
                subscribers.forEach(function(elem){
                     elem.onMessage(data);
                });
            }
       };
})();

Script 1:

(function(pubsub){
     var someObject = {}; // to share state
     //code here
     pubsub.subscribe(someObject);

     someObject.onMessage = function(){
        //whatever you do when you get a message
     };
})(window.pubsub);

Script 2 would be identical, only it would handle messages differently.

This way, you have one global variable (if that's too much, you can even delete window's reference to it after subscribing script 2, which would mean no globals at all)

*technically try/catch and with also introduce scope, but they're very rare and should not be used like this

Upvotes: 2

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