ByPasser overview

This module implements a type that can optionally short-circuit the normal stringification pipeline for a given non-primitive value. When a PPByPasser decides to handle a value it returns a some of the resulting string, bypassing the usual property-extraction and formatting steps. When it does not apply, it returns a none and the normal pipeline takes over.

A typical use case is printing a Date as a human-readable string rather than as an object with all its internal properties.

Use the make function to define custom instances if the pre-built ones do not suit your needs.

Table of contents

• Constructors
  • make
  • merge
• Equivalences
  • equivalence
• Getters
  • action
  • id
• Instances
  • allWithName
  • dateAndRegExp
  • empty
  • toStringable
• Models
  • Type (class)
    • [MData.idSymbol] (method)
    • [Hash.symbol] (method)
    • [MEquivalenceBasedEqualityData.isEquivalentToSymbol] (method)
    • [MEquivalenceBasedEqualityData.hasSameTypeMarkerAsSymbol] (method)
    • id (property)
    • action (property)
• Module markers
  • moduleTag

Constructors

make

Constructor of a PPByPasser

Signature

export declare const make: (params: MTypes.Data<Type>) => Type

merge

Creates a new PPByPasser by composing several existing PPByPasser’s. The resulting PPByPasser returns the some of the first PPByPasser in byPassers that returns a some for the given value. Returns none if no PPByPasser matches.

Signature

export declare const merge: ({
  id,
  byPassers
}: {
  readonly id: string
  readonly byPassers: ReadonlyArray<Type>
}) => Type

Equivalences

equivalence

Equivalence

Signature

export declare const equivalence: Equivalence.Equivalence<Type>

Getters

action

Returns the action property of self

Signature

export declare const action: MTypes.OneArgFunction<
  Type,
  MTypes.OneArgFunction<
    {
      readonly nonPrimitive: PPValue.ReadonlyNonPrimitive
      readonly parameters: PPParameters.Type
      readonly applicableNonPrimitiveParameters: PPResolvedNonPrimitiveParameters.Type
    },
    Option.Option<string>
  >
>

id

Returns the id property of self

Signature

export declare const id: MTypes.OneArgFunction<Type, string>

Instances

allWithName

PPByPasser instance that displays the non-primitive value as its name surrounded by the openingTagMark and closingTagMark (e.g. [Function: foo]). Always returns a some. Can be used to display functions.

Signature

export declare const allWithName: Type

dateAndRegExp

PPByPasser instance that:

• Returns a some of the result of calling .toISOString() on a Date non-primitive value
• Returns a some of the result of calling .toString() on a RegExp non-primitive value
• Returns a none for all other non-primitive values

This is the default byPasser baked into the merge defaults, so dates and regular expressions are pretty-printed as 2026-04-29T00:00:00.000Z and /foo/g even when no PPNonPrimitiveParameters explicitly sets a byPasser.

Signature

export declare const dateAndRegExp: Type

empty

PPByPasser instance that never bypasses any value (always returns none)

Signature

export declare const empty: Type

toStringable

PPByPasser instance that calls the .toString() method of the non-primitive value, but only when that method is not Object.prototype.toString (i.e. the value has a custom or overridden implementation). Returns a some of the result on success, none otherwise.

Practical examples where this returns a some: Date, any class that overrides toString. Note that calling .toString() on a function will return its source code, which is usually not the desired output.

Signature

export declare const toStringable: Type

Models

Type (class)

Type that represents a PPByPasser

Signature

export declare class Type {
  constructor({ id, action }: MTypes.Data<Type>)
}

[MData.idSymbol] (method)

Returns the id of this

Signature

[MData.idSymbol](): string | (() => string)

[Hash.symbol] (method)

Calculates the hash value of this

Signature

[Hash.symbol](): number

[MEquivalenceBasedEqualityData.isEquivalentToSymbol] (method)

Function that implements the equivalence of this and that

Signature

[MEquivalenceBasedEqualityData.isEquivalentToSymbol](this: this, that: this): boolean

[MEquivalenceBasedEqualityData.hasSameTypeMarkerAsSymbol] (method)

Predicate that returns true if that has the same type marker as this

Signature

[MEquivalenceBasedEqualityData.hasSameTypeMarkerAsSymbol](that: unknown): boolean

id (property)

Id of this PPByPasser instance. Useful for equality and debugging

Signature

readonly id: string

action (property)

Action of this PPByPasser. Takes as input:

• nonPrimitive: the non-primitive value being stringified (used as context for styling),
• parameters: the PPParameters instance passed to the PPStringifier,
• applicableNonPrimitiveParameters: the merged, fully-resolved PPNonPrimitiveParameters fields applicable to nonPrimitive (see PPResolvedNonPrimitiveParameters.fromApplicableNonPrimitiveParameters).

Returns Option.some(s) where s is the bypass string when this bypasser handles the value.

Signature

readonly action: MTypes.OneArgFunction<{ readonly nonPrimitive: PPValue.ReadonlyNonPrimitive; readonly parameters: PPParameters.Type; readonly applicableNonPrimitiveParameters: PPResolvedNonPrimitiveParameters.Type; }, Option.Option<string>>

Module markers

moduleTag

Module tag

Signature

export declare const moduleTag: "@parischap/pretty-print/Parameters/ByPasser/"