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 = '';
    }

}

Called in HTML like

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

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=''){}

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

function name(p_Para1, p_Para2) {
if (p_Para1 == null) {
    p_Para1 = defaultval1;
}
if (p_Para2 == null) {
    p_Para2 = defaultval2;
}
// rest of function
}

@chrishirst - thank much.

Also i found i can add this to my function.

if (typeof token != 'undefined')

Here is a more elegant solution.

The reason this works is that the logical OR of JavaScript returns values in left to right precedence when assigning values. You can simply do something like this (I'm using a more extreme example where the input is a whole object with several properties):

function myFunction(obj) {
var defaults = {
     prop1: "hello",
     prop2: "world",
     prop3: "goodbye",
     prop4: "world"
}
//the magic
obj = obj || defaults;
//logic goes here...
}

Of course, this will work with any value, not just a set of objects. Set a default then say {variable = variable || default} where variable is the function input.