Comments on: JavaScript – Creating Default Arguments

By: Maat

Maat — Fri, 12 Jun 2009 08:12:58 +0000

IMO it is more readable/understandable to use the “arguments” variable and it allows more flexibility. Something like:

function lorum(/*x, y*/) {
var x;
var y;
switch(arguments.length) {
case 0 :
x = 100;
y = 500;
break
case 1 :
x = arguments[0];
y = 500;
break
case 2 :
x = arguments[0];
y = arguments[1];
break;
}
// …
}

By: k4st

k4st — Tue, 09 Jun 2009 22:00:41 +0000

Ah, very good point; I hadn’t thought of that. Thank you.

By: geekfreak

geekfreak — Tue, 09 Jun 2009 18:37:43 +0000

oops…

function flag(flag){
return flag || true;
}

flag(true) == flag(false) == flag();

By: geekfreak

geekfreak — Tue, 09 Jun 2009 18:11:46 +0000

The typeof === undefined comparision is better as it will not cause problems with boolean (or falsey) parameter values.

function foo(flag){
return flag || true;
}

flag(true) == flag(false) == flag();

a corner case for sure, but certainly a failure case for the boolean operand strategy

By: cancel bubble

cancel bubble — Tue, 09 Jun 2009 15:03:35 +0000

You should be declaring your variables with var inside the function, otherwise you’re creating global variables and are much more likely to have name collisions. vars inside a function are “private”, a variable declared within a function is not accessible outside of that function.

function ipsum(i, j) {
var i = i || 100;
var j = j || 500;

// or in one var declaration

var i = i || 100, j = j || 500
}

By: contantofaz

contantofaz — Tue, 09 Jun 2009 14:57:50 +0000

If i or j is meant to be set to 0 by the end-user, this code will not allow that:

function tell_it(i, j){
i = i === undefined ? 100 : i;
j = j === undefined ? 500 : j;
system.k7.shell.print(i);
system.k7.shell.print(j);
}

function say_what(i, j){
i = i || 100;
j = j || 500;
system.k7.shell.print(i);
system.k7.shell.print(j);
}

system.k7.shell.print(‘—– say what’);

say_what();
say_what(1, 2);
say_what(0, 3);

system.k7.shell.print(‘—– tell it’);

tell_it();
tell_it(1, 2);
tell_it(0, 3);

Outputs:

$ k7 js_is_cool.js
—– say what
100
500
1
2
100
3
—– tell it
100
500
1
2
0
3

By: contantofaz

contantofaz — Tue, 09 Jun 2009 14:57:50 +0000

If i or j is meant to be set to 0 by the end-user, this code will not allow that:

function tell_it(i, j){
i = i === undefined ? 100 : i;
j = j === undefined ? 500 : j;
system.k7.shell.print(i);
system.k7.shell.print(j);
}

function say_what(i, j){
i = i || 100;
j = j || 500;
system.k7.shell.print(i);
system.k7.shell.print(j);
}

system.k7.shell.print(‘—– say what’);

say_what();
say_what(1, 2);
say_what(0, 3);

system.k7.shell.print(‘—– tell it’);

tell_it();
tell_it(1, 2);
tell_it(0, 3);

Outputs:

$ k7 js_is_cool.js
—– say what
100
500
1
2
100
3
—– tell it
100
500
1
2
0
3

By: k4st

k4st — Tue, 09 Jun 2009 10:19:05 +0000

In fact, you can shorten that in Javascript to:

i = i || 100;
j = j || 500;

By: contantofaz

contantofaz — Tue, 09 Jun 2009 07:24:15 +0000

What are the drawbacks to checking whether the variable exists more directly with:

function ipsum(i, j) {

i = i === undefined ? 100 : i;
j = j === undefined ? 500 : j;

// …
}

By: Peter Goodman

Peter Goodman — Tue, 09 Jun 2009 05:19:55 +0000

Or even shorter:

i = i || 100;
j = j || 500;