ifndef

$$ifndef is the counterpart of $$ifdef: it keeps its value while a define flag is not set, and removes it, along with every reference to the name it bound, while the flag is.

🧠 Add the types

$$ifndef is declared globally by the package. Add it to types in tsconfig.json so TypeScript knows about it.

{
    "compilerOptions": {
        "types": [ "node", "@remotex-labs/xbuild" ]
    }
}

Syntax

$$ifndef('FLAG', valueOrCallback)

Argument	Type	Notes
FLAG	string literal	Required, and a literal rather than a variable.
valueOrCallback	unknown	Required. A function, an expression, or a literal.

When a flag counts as unset

The same table $$ifdef reads, answered the other way round.

define entry	$$ifndef keeps its value
PROD: false	yes
PROD: null	yes
PROD: undefined	yes
not named at all	yes
PROD: true	no
PROD: 0	no - '0' is text
PROD: ''	no - so is the empty string
PROD: 'anything'	no

🔢 0 and '' set the flag in 3.0.0

v2 decided on truthiness, so PROD: 0 kept an $$ifndef value. 3.0.0 decides on the substituted text, and only false, null, undefined, and an absent key leave a flag unset. Write false where 0 used to mean off.

Forms

Identical to $$ifdef. How the second argument is written decides the shape:

export const $$devOnly = $$ifndef('PROD', () => console.log('dev mode'));

// PROD unset
export function $$devOnly() { return console.log('dev mode'); }

// PROD set - the declaration is removed, and every read of $$devOnly becomes undefined

A function the source invokes stays invoked:

const $$label = $$ifndef('PROD', (name: string) => `${ name } dev`)('build');
// PROD unset: const $$label = ((name: string) => `${ name } dev`)('build');

A macro standing as a statement has its body inlined:

$$ifndef('PROD', () => {
    installDevTools();
});
// PROD unset: installDevTools();
// PROD set:   nothing

A literal or an expression is substituted as written:

export const $$assertions = $$ifndef('PROD', true);
// PROD unset: export const $$assertions = true;

The two together

Write both to get a value either way, and only one of them survives any given build:

export const $$log = $$ifndef('PROD', (message: string) => console.log(message));
export const $$noop = $$ifdef('PROD', () => undefined);

Dropping reaches across files

Exactly as with $$ifdef: a name dropped where it was declared is pruned from the imports that name it, and its reads become undefined. See Dropping reaches across files.

🔍 Seeing the replacements

Run with logLevel: 'verbose', or press v in a watching run, to see what each macro was replaced with.

See also

• ifdef - the same, on the opposite answer.
• inline - evaluate at build time and substitute the result.
• define - where the flags come from.