JS: functions arguments default values

Question

In some languages you can set default values for function\'s arguments:

function Foo(arg1 = 50, arg2 = \'default\') {
    //...
}

How do yo

Answer 1

You would have to do it in the function body:

function Foo(arg1 ,arg2) {
    if( typeof arg1 === 'undefined' )
        arg1 = 50;

    if( typeof arg2 === 'undefined' )
        arg2 = 'default';
    //...
}

Another way to test them for undefined or null is like this:

function Foo(arg1 ,arg2) {
    if( arg1 == undefined )
        arg1 = 50;

    if( arg2 == undefined )
        arg2 = 'default';
    //...
}

Some people don't like it because it is possible to override the value of undefined since it is just a global property. As long as it isn't overridden, this would work fine. If the parameters are null or undefined, they'll be set to a default.