Empty Function Paramaters

How do i declare a default value in a function? I have a simple function

function color_input(id,token){

	if (!empty(token)){
		document.getElementById(id).style.backgroundColor = '#2A2A2A';
		document.getElementById(id).style.color = '#DDC58C';
	}else{
		document.getElementById(id).style.backgroundColor = '';
		document.getElementById(id).style.color = '';
	}

}

Code (markup):

Called in HTML like

<input type="text" id="example_name" onblur="color_input('example_name');">

HTML:

You will notice that the #2 parameter is missing in the html call. Sometimes i don't have it to send. in PHP i would just set the functions second param like token=''

function color_input(id,token=''){}

Code (markup):

How do i set a default param in a JS function?

 

Hi,

you can either use function color_input(id){ ... and then check for #2 parameter as if(!empty(arguments[1])) ... }
or you can keep it as you have it - function color_input(id,token){} and when you call this function you always fill the token value - null, or '' if not needed - <input type="text" id="example_name" onblur="color_input('example_name',null);">

 

You cannot assign default values to javascript functions. This is very annoying, but the easiest solution is quite simple. Assuming you have a function that has two parameters, but you call it with just one (just like you did in your code), but you want to have a default value for the parameters, you can do something like this:

function test(param1, param2)
{
   if(!param1)
      param1 = 'default';

   //or

   if(param2 == 'undefined')
     param2 = 1;
}

Code (markup):

Then, if you call the function with just one parameter - param2 will have the value of 1. If you call it without parameters, param1 will be 'default' and param2 will be 1... If a parameter is not set when you call the function, the variable exists within the function scope, but is 'undefined'.

 

@lp1501 - thanks for your suggestion.

This will be easier though to add this to my function.

if (typeof token != 'undefined')

Code (markup):

 

yep, this is another way to check if the parameter is not set. Javascript variables and types are veeery weird, thus all three methods work for checking if a parameter is passed or not

 

you can do:

function func(arg)
{
  arg = (arg == undefined ? 'default value' : arg);
}

Code (markup):

 

what i tend to do is use json and merge options... for instance:

// in mootools, you can use $merge...
var foobar = function(options) {
    var options = $merge({
        "token": "2",
        "margin": "150px",
        "title": "My title"
    }, options);
     
    console.log(options.title, options.margin); // will output 'new title' and '150px'
    console.log(options); // will output the whole object complete with token's default as well
};

foobar({
    title: "new title"
});

// or run as default values only...
foobar();

PHP:

the advantages are that you can add as many params as you need to via the function call, you don't need to pre-define them in the function definition or anything like that, no relying on the arguments' order - each option has a name space you can find easily.