declared

declared is a module for setting default values for optional arguments.

Actually, it is a bit more general than that. It takes a bunch of values, and simply returns the first value that is "!= undefined".

The problem it is solving is that in JavaScript the argument is considered omitted if it is either null or undefined (common convention), but there's no built-in operator for this.

The closest thing is logical or (||), but it is not quite what we want.

> '' || 'default'
'default'

This module is a counterpart to @substack's defined which checks for strong equality for some reason (and does not work for nulls).

Example

// Say description is optional.
function describe(name, description) {
  description = declared(description, 'coolest thing ever!');
  return [name, description];
}

> describe('x', 'my description')
[ 'x', 'my description' ]
> describe('x', '')
[ 'x', '' ]

// null and undefined both stand for the default value.
> describe('x', null)
[ 'x', 'coolest thing ever!' ]
> describe('x', undefined)
[ 'x', 'coolest thing ever!' ]

API

declared([value]...)

Return the first argument that is "!= undefined" (or "!= null", which is the same thing). If all arguments are undefined, just return undefined.

Equivalent chain of conditional statements:

if (value0 != null) {
  return value0;
}
else if (value1 != null) {
  return value1;
}
/* ... */
else if (valueN != null) {
  return valueN;
}
else {
  return undefined;
}

Install

npm install declared

License

MIT