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I'm sure, this question has been answered somewhere before but I just couldn't find it.

If within a function a variable has been defined, what is the best practice to save it for later use? 1. Saving it "globally"?
foo = 'bar';
...
function bar(){
...
foo = 'bat';
return foo;
}
...

Here, the variable will be altered later on. 2. Or saving it within a hidden form field within the HTML-DOM?

`Thanxs!

I'm sure, this question has been answered somewhere before but I just couldn't find it.

If within a function a variable has been defined, what is the best practice to save it for later use? 1. Saving it "globally"?
foo = 'bar';
...
function bar(){
...
foo = 'bat';
return foo;
}
...

Here, the variable will be altered later on. 2. Or saving it within a hidden form field within the HTML-DOM?

`Thanxs!

• javascript
• jquery

Share Improve this question Follow edited Oct 25, 2010 at 11:18 Mike asked Oct 25, 2010 at 10:59 MikeMike 2311 silver badge44 bronze badges 6

• Depends on how it is to be used and why. If its only to be used in the same function you could store it as a property on the function name bar["foo"] = "", but if it is to be used elsewhere it might be better to declare it there fro mthe beginning. – David Mårtensson Commented Oct 25, 2010 at 11:03
• Note: I think you might want to edit it to say foo = "bar"; function bar(){ ... foo = "bat"; return foo; }. At least that is how I read the question. – BudgieInWA Commented Oct 25, 2010 at 11:07
• This is en exaple of how I thought: function c() { if(typeof c["1"] == "undefined") c["1"] = 1; document.write(c["1"]++); } c(); It works as a static variable. – David Mårtensson Commented Oct 25, 2010 at 11:10
• By the way, how do I highlight code in ments ;) – David Mårtensson Commented Oct 25, 2010 at 11:12
• @David Mårtensson, Backticks surrounding your code. (The key is probably just below your ESC key). Looks like this: ` (This can be used for inline code in Qs and As too) – BudgieInWA Commented Oct 25, 2010 at 11:20

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3 Answers 3

Sorted by: Reset to default 2

Saving it as a global JavaScript variable is by far the most efficient.

EDIT: If the data you want to save is associated with an element on the page (for example, each row in a table has a bit of data associated with it), and you are using jQuery, there is a data() method which is more efficient than setting an attribute on the element or something similar.

It depends on the context, but probably: In a variable defined at the top level of a closure that wraps the set of functions to which it applies.

i.e.

var exports = function () {
    var stored_data;
    function set_data(foo) {
        stored_data = foo;
    }
    function get_data() {
        return stored_data;
    }
    return { get: get_data, set: set_data };
}();

This avoids the risk of other scripts (or other parts of your own, potentially very large, script) overwriting it by accident.

The HTML5 spec has defined a solution to this question: If you are using HTML5, you can specify data attributes in your DOM.

See this page for more info: http://ejohn/blog/html-5-data-attributes/

This is now the standardised way of doing it, so I guess that it's considered best practice. Also John Resig, who wrote the blog I linked to above, is the author of JQuery, so if it's good enough for him, who am I to argue.

The really good news is that you don't even have to be using an HTML5-patible browser for this technique to work - it already works in older browsers; it's just that now it's been encoded into the standard, and there's a defined way to do it.

That said, there's nothing wrong with a global variable in your Javascript as long as you avoid polluting the namespace too much, and it would be more efficient from a performance perspective, so there's plenty of merit in that approach as well.

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