Javascript/Jquery - Setting default value in function

Question

Using javascript/jquery is there a way to set a variable to a default value if no value is passed in the function? For example

function someFunction(data1,data2)
{


}

If data1 or data 2 is empty it gives me an undefined value. In php I could do just this:

function somefunction(data1 = '',data2 = '')
{


}

So if no variable is passed or data1 or data 2 it defaults to ''. In JS/Jquery do I have to check if there is a value and set it accordingly?

function someFunction(data1,data2)
{

if(!data1) {

data1 = '';

}

if(!data2) {

data2 = ''

}

}

Just seems alot needs to be done to check if variable is empty or not to give it a default value.

Amber · Accepted Answer · 2011-10-15 06:59:32Z

27

function foo(bar) {
    bar = bar || 'default';
}

(Alternatively, if you only ever use bar once, you can just replace that usage with bar || <default value> and skip the intermediate assignment.)

answered Oct 15, 2011 at 6:59

Amber

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1 Comment

Felix Kling Over a year ago

This works as long as bar is not allowed to have a value which evaluates to false. In this case, the longer ternary operator has to be used (to compare against the "invalid" value explicitly).

Christian P · Accepted Answer · 2011-10-15 07:10:57Z

4

function someFunction(data){
    data = data || 'my value';
}

The only problem with this is that the 0, false and undefined are treated the same:

someFunction(1); // data = 1;
someFunction(-1); // data = -1;
someFunction(); // data = 'my value';
someFunction(0); // data = 'my value';
someFunction(false); // data = 'my value';

answered Oct 15, 2011 at 7:10

Christian P

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Comments

Maurizio In denmark · Accepted Answer · 2013-06-24 08:49:43Z

4

You can use this:

function foo(optionalArg) {
    optionalArg = optionalArg|| 'defaultValue';
}

as long as you never pass a value to the parameter. This logic fails if optionalArg is passed Try this instead:

function foo(optionalArg) {
    optionalArg = (typeof optionalArg === "undefined") ? "defaultValue" : optionalArg;
}

answered Jun 24, 2013 at 8:49

Maurizio In denmark

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Comments

Deeptechtons · Accepted Answer · 2011-10-15 07:06:30Z

2

You would use jquery's extend method but define defaults in the code like below

$.fn.myPlugin = function (settings) {
    var options = jQuery.extend({
        name: "MyPlugin",
        target: document,
        onOpen: function () {},
        onClose: function () {},
        onSelect: function () {}
    }, settings);
}

now you could do

$("#divId").myPlugin({
    target: $("#div2")
};

this will now override the document target defined inside the defaults with element having div2 as id.

answered Oct 15, 2011 at 7:06

Deeptechtons

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2 Comments

bean5 Over a year ago

I think this would only work for functions in jQuery plugins, right?

Deeptechtons Over a year ago

@bean5 Yes correct. If you want to build something that has to do with configuration and defaults i bet that piece of code is well worth written as plugin than global function.

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