fields

fields holds values for one Jest config field each. The known* members are ready-made values. The define* functions wrap a value in its field name.

import { fields } from '@repobuddy/jest'

Member	Field	Kind
knownTestEnvironments	testEnvironment	object
knownExtensionsToTreatAsEsm	extensionsToTreatAsEsm	object
knownModuleNameMappers	moduleNameMapper	object
defineModuleNameMappers()	moduleNameMapper	function
knownTransforms.swc()	transform	function
knownTransforms.tsJest()	transform	function
knownTransforms.tsJestCjs()	transform	function
knownTransforms.tsJestEsm()	transform	function
knownTransforms.esmPackages()	transform	function
defineTransform()	transform	function
knownWatchPlugins	watchPlugins	object of functions
watchPlugins	watchPlugins	array
defineWatchPlugins()	watchPlugins	function

The package also exports the types Transform, Transform.TsJestOptions, Transform.TransformerConfig, WatchPlugins, WatchPlugins.BaseOptions, WatchPlugins.SuspendOptions, and WatchPlugins.ToggleConfig from this namespace.

knownTestEnvironments

{ jsdom: 'jsdom', node: 'node' }

knownExtensionsToTreatAsEsm

{
  js: ['.jsx'],
  ts: ['.ts', '.mts', '.tsx'],
}

configs.tsEsm uses ts. configs.jsEsm uses js.

knownModuleNameMappers

Key	Value	Use
tsEsm	{ '^(\\.{1,2}/.*)\\.js$': '$1' }	Map a relative ./x.js import to ./x, so TypeScript ESM source resolves.
cssAll	{ '\\.module\\.css$': 'identity-obj-proxy', '.+\\.(css|styl|less|sass|scss)$': 'identity-obj-proxy' }	Map style imports to identity-obj-proxy. Needs the identity-obj-proxy package.

No preset uses cssAll. Add it yourself (see DOM tests with jsdom).

defineModuleNameMappers()

Merges mapper objects into one.

function defineModuleNameMappers(...entries: Array<Record<string, string>>): Record<string, string>

Parameter	Type	Default	Effect
...entries	Record<string, string>[]	none	Mapper objects. A later entry wins on the same key.

Returns a new object. It does not wrap the result in { moduleNameMapper }.

From the spec:

fields.defineModuleNameMappers(fields.knownModuleNameMappers.tsEsm, fields.knownModuleNameMappers.cssAll)
// {
//   '^(\\.{1,2}/.*)\\.js$': '$1',
//   '\\.module\\.css$': 'identity-obj-proxy',
//   '.+\\.(css|styl|less|sass|scss)$': 'identity-obj-proxy',
// }

knownTransforms.swc()

@swc/jest for every JavaScript and TypeScript extension.

swc(options?: Record<string, unknown>): Record<string, string | [string, Record<string, unknown>]>

Parameter	Type	Default	Effect
options	Record<string, unknown>	none	Passed to @swc/jest. Without it, the entry is the bare name.

fields.knownTransforms.swc()
// { '^.+\\.(js|jsx|cjs|mjs|ts|tsx|cts|mts)$': '@swc/jest' }

fields.knownTransforms.swc({ jsc: { target: 'es2022' } })
// { '^.+\\.(js|jsx|cjs|mjs|ts|tsx|cts|mts)$': ['@swc/jest', { jsc: { target: 'es2022' } }] }

knownTransforms.tsJest()

ts-jest for .ts, .tsx, .cts, .mts, with the options you pass and no defaults.

tsJest(options: Transform.TsJestOptions): Record<string, string | [string, Record<string, unknown>]>

Parameter	Type	Default	Effect
options	Transform.TsJestOptions	required	Passed to ts-jest.

Transform.TsJestOptions types these ts-jest options: compiler, tsconfig, isolatedModules, astTransformers, diagnostics (boolean or { ignoreCodes }), babelConfig, stringifyContentPathRegex, useESM.

fields.knownTransforms.tsJest({ tsconfig: 't.json' })
// { '^.+\\.(ts|tsx|cts|mts)$': ['ts-jest', { tsconfig: 't.json' }] }

knownTransforms.tsJestCjs()

ts-jest with isolatedModules: true, plus esmPackages(). The ts-cjs presets use it.

tsJestCjs(options?: Transform.TsJestOptions): Record<string, string | [string, Record<string, unknown>]>

Parameter	Type	Default	Effect
options	Transform.TsJestOptions	none	Merged over { isolatedModules: true }.

From the spec:

fields.knownTransforms.tsJestCjs()
// {
//   '^.+\\.(ts|tsx|cts|mts)$': ['ts-jest', { isolatedModules: true }],
//   '\\.m?jsx?$': 'jest-esm-transformer-2',
// }

Your options keep the default unless you set it:

fields.knownTransforms.tsJestCjs({ isolatedModules: false })
// {
//   '^.+\\.(ts|tsx|cts|mts)$': ['ts-jest', { isolatedModules: false }],
//   '\\.m?jsx?$': 'jest-esm-transformer-2',
// }

knownTransforms.tsJestEsm()

ts-jest with isolatedModules: true and useESM: true. No preset uses it. It is the way to run TypeScript ESM through ts-jest instead of SWC.

tsJestEsm(options?: Transform.TsJestOptions): Record<string, string | [string, Record<string, unknown>]>

Parameter	Type	Default	Effect
options	Transform.TsJestOptions	none	Merged over { isolatedModules: true, useESM: true }.

From the spec:

fields.knownTransforms.tsJestEsm()
// { '^.+\\.(ts|tsx|cts|mts)$': ['ts-jest', { isolatedModules: true, useESM: true }] }

knownTransforms.esmPackages()

jest-esm-transformer-2 for .js, .jsx, .mjs, .mjsx. Pair it with transformIgnorePatterns: [] so it reaches node_modules.

esmPackages(): Record<string, string>

Parameters: none.

fields.knownTransforms.esmPackages()
// { '\\.m?jsx?$': 'jest-esm-transformer-2' }

Calling knownTransforms methods

tsJestCjs() and tsJestEsm() call this.tsJest(). Call them on the object. A destructured call fails:

const { tsJestCjs } = fields.knownTransforms
tsJestCjs()
// TypeError: Cannot read properties of undefined (reading 'tsJest')

defineTransform()

Wraps a transform map in { transform }, typed as Jest’s transform field.

function defineTransform(transform: Transform): { transform: Transform }

Parameter	Type	Default	Effect
transform	Transform (Jest’s Config['transform'])	required	The transform map.

fields.defineTransform(fields.knownTransforms.swc())
// { transform: { '^.+\\.(js|jsx|cjs|mjs|ts|tsx|cts|mts)$': '@swc/jest' } }

knownWatchPlugins

Functions that return one watchPlugins entry. Each returns the bare name without options, or [name, options] with options.

Function	Package entry	Options type
suspend(options?)	jest-watch-suspend	WatchPlugins.SuspendOptions: key, prompt, 'suspend-on-start'
toggleConfig(options?)	jest-watch-toggle-config	WatchPlugins.ToggleConfig: key, prompt, setting (required in the type)
typeaheadFilename(options?)	jest-watch-typeahead/filename	WatchPlugins.BaseOptions: key, prompt
typeaheadTestname(options?)	jest-watch-typeahead/testname	WatchPlugins.BaseOptions: key, prompt

From the spec:

fields.knownWatchPlugins.suspend({ 'suspend-on-start': true })
// ['jest-watch-suspend', { 'suspend-on-start': true }]

fields.knownWatchPlugins.toggleConfig({ setting: 'bail' })
// ['jest-watch-toggle-config', { setting: 'bail' }]

watchPlugins

The default plugin list. The watch preset and every -watch preset use it.

[
  'jest-watch-suspend',
  ['jest-watch-toggle-config', { setting: 'collectCoverage' }],
  ['jest-watch-toggle-config', { setting: 'verbose' }],
  'jest-watch-typeahead/filename',
  'jest-watch-typeahead/testname',
]

defineWatchPlugins()

Wraps a plugin list in { watchPlugins }.

function defineWatchPlugins(config?: WatchPlugins): { watchPlugins: WatchPlugins }

Parameter	Type	Default	Effect
config	WatchPlugins (Jest’s Config['watchPlugins'])	watchPlugins	The plugin list.

fields.defineWatchPlugins([
  fields.knownWatchPlugins.suspend({ 'suspend-on-start': true }),
  fields.knownWatchPlugins.typeaheadFilename({ key: 'f' }),
])
// {
//   watchPlugins: [
//     ['jest-watch-suspend', { 'suspend-on-start': true }],
//     ['jest-watch-typeahead/filename', { key: 'f' }],
//   ],
// }

Related

• configs
• Customize a preset