pretty-format
Advanced tools
Package description
The pretty-format npm package is a JavaScript library that allows you to serialize any JavaScript value into a string with a human-readable format. It is particularly useful for snapshot testing, where you want to compare the expected and actual output of your test cases.
Pretty-printing of basic JavaScript types
This feature allows you to convert basic JavaScript types like objects, arrays, strings, numbers, etc., into a nicely formatted string.
const prettyFormat = require('pretty-format');
const value = { foo: 'bar', baz: 42 };
console.log(prettyFormat(value));Customizing output with plugins
pretty-format supports plugins that can be used to customize the output for specific types of values, such as React elements.
const prettyFormat = require('pretty-format');
const ReactElementPlugin = require('pretty-format/plugins/ReactElement');
const reactElement = <div>Hello World</div>;
console.log(prettyFormat(reactElement, { plugins: [ReactElementPlugin] }));Minimizing diff output
By using pretty-format in combination with a diffing library like jest-diff, you can minimize the output of diffs to make them easier to read and understand.
const prettyFormat = require('pretty-format');
const diff = require('jest-diff');
const oldValue = { a: 'old', b: 'values' };
const newValue = { a: 'new', b: 'values' };
const difference = diff(prettyFormat(oldValue), prettyFormat(newValue));
console.log(difference);Chalk is a popular npm package for styling terminal strings. While it doesn't serialize objects, it can be used in conjunction with pretty-format to colorize the output, enhancing readability.
Util is a core Node.js module that provides a method called 'inspect' for printing objects in a readable format. It is similar to pretty-format but is built into Node.js and does not support plugins.
js-beautify is an npm package that can format HTML, CSS, and JavaScript code. It is more focused on formatting code rather than serializing arbitrary JavaScript values like pretty-format.
Changelog
24.3.0
We skipped 24.2.0 because a draft was accidentally published. Please use 24.3.0 or a newer version instead.
[expect]: Improve report when matcher fails, part 10 (#7960)[expect]: Improve report when matcher fails, part 11 (#8008)[expect]: Improve report when matcher fails, part 12 (#8033)[expect]: Improve report when matcher fails, part 7 (#7866)[expect]: Improve report when matcher fails, part 8 (#7876)[expect]: Improve report when matcher fails, part 9 (#7940)[jest-circus/jest-jasmine2] Warn if describe returns a value (#7852)[jest-config] Print error information on preset normalization error (#7935)[jest-get-type] Add isPrimitive function (#7708)[jest-haste-map] Add skipPackageJson option (#7778)[jest-util] Add isPromise (#7852)[pretty-format] Support React.memo (#7891)[expect] Fix toStrictEqual not considering arrays with objects having undefined values correctly (#7938)[expect] Fix custom async matcher stack trace (#7652)[expect] Fix non-object received value in toHaveProperty (#7986, #8067)[expect] Fix non-symmetric equal for Number (#7948)[expect] Remove duck typing and obsolete browser support code when comparing DOM nodes and use DOM-Level-3 API instead (#7995)[jest-changed-files] Fix getChangedFilesFromRoots to not return parts of the commit messages as if they were files, when the commit messages contained multiple paragraphs (#7961)[jest-changed-files] Fix pattern for HG changed files (#8066)[jest-changed-files] Improve default file selection for Mercurial repos (#7880)[jest-circus] Fix bug with test.only (#7888)[jest-circus]: Throw explicit error when errors happen after test is considered complete (#8005)[jest-cli] Fix prototype pollution vulnerability in dependency (#7904)[jest-cli] Refactor -o and --coverage combined (#7611)[jest-environment-node] Add missing globals: TextEncoder and TextDecoder (#8022)[jest-haste-map] Enforce uniqueness in names (mocks and haste ids) (#8002)[jest-jasmine2]: Throw explicit error when errors happen after test is considered complete (#8005)[jest-mock] Adds a type check to prototype to allow mocks of objects with a primitive prototype property. (#8040)[jest-transform] Normalize config and remove unnecessary checks, convert TestUtils.js to TypeScript (#7801)[jest-util]Make sure to not fail if unable to assign toStringTag to the process object, which is read only in Node 12 (#8050)[jest-validate] Fix validating async functions (#7894)[jest-worker] Fix jest-worker when using pre-allocated jobs (#7934)[static] Remove console log '-' on the front page (#7977)[*]: Setup building, linting and testing of TypeScript (#7808, #7855, #7951)[@jest/console]: Extract custom console implementations from jest-util into a new separate package (#8030)[@jest/core] Create new package, which is jest-cli minus yargs and prompts (#7696)[@jest/core]: Migrate to TypeScript (#7998)[@jest/fake-timers]: Extract FakeTimers class from jest-util into a new separate package (#7987)[@jest/reporter]: New package extracted from jest-cli (#7902)[@jest/reporters]: Migrate to TypeScript (#7994, #8045)[@jest/source-map]: Extract getCallsite function from jest-util into a new separate package (#8029)[@jest/test-result]: Extract TestResult types and helpers into a new separate package (#8034)[@jest/transform]: Migrate to TypeScript (#7918, #7945)[@jest/transform]: New package extracted from jest-runtime (#7915)[@jest/types]: New package to handle shared types (#7834)[babel-jest]: Migrate to TypeScript (#7862)[babel-plugin-jest-hoist]: Migrate to TypeScript (#7898)[diff-sequences]: Migrate to Typescript (#7820)[docs] Add missing import to docs (#7928)[docs] Update automock configuration, add note related to manual mocks (#8051)[docs] Update/Organize TestSequencer and testSchedulerHelper code comments(#7984)[docs]: Fix image paths in SnapshotTesting.md for current and version 24 (#7872)[docs]: Improve runAllTimers doc (it exhausts the micro-task queue) (#8031)[docs]: Update CONTRIBUTING.md to add information about running jest with jest-circus locally (#8013).[expect]: Migrate to TypeScript (#7919, #8028)[jest-changed-files]: Migrate to TypeScript (#7827)[jest-circus]: Migrate to TypeScript (#7916)[jest-cli]: Migrate to TypeScript (#8024)[jest-diff]: Migrate to TypeScript (#7824, #8027)[jest-docblock]: Migrate to TypeScript (#7836)[jest-each]: Migrate to Typescript (#8007)[jest-each]: Refactor into multiple files with better types (#8018)[jest-environment-jsdom]: Migrate to TypeScript (#8003)[jest-environment-node]: Migrate to TypeScript (#7985)[jest-get-type]: Migrate to TypeScript (#7818)[jest-haste-map]: Migrate to TypeScript (#7854, #7951)[jest-jasmine2]: TS migration (#7970)[jest-leak-detector]: Migrate to TypeScript (#7825)[jest-matcher-utils]: Migrate to TypeScript (#7835)[jest-message-util]: Migrate to TypeScript (#7834)[jest-mock]: Migrate to TypeScript (#7847, #7850, #7971)[jest-phabricator]: Migrate to TypeScript (#7965)[jest-regex-util]: Migrate to TypeScript (#7822)[jest-repl]: Migrate to TypeScript (#8000)[jest-resolve-dependencies]: Migrate to TypeScript (#7922)[jest-resolve]: Migrate to TypeScript (#7871)[jest-runner]: Migrate to TypeScript (#7968)[jest-runtime]: Migrate to TypeScript (#7964, #7988)[jest-serializer]: Migrate to TypeScript (#7841)[jest-snapshot]: Migrate to TypeScript (#7899)[jest-util]: Migrate to TypeScript (#7844, #8021)[jest-validate]: Migrate to TypeScript (#7991)[jest-watcher]: Migrate to TypeScript (#7843)[jest-worker]: Migrate to TypeScript (#7853)[jest]: Migrate to TypeScript (#8024)[pretty-format]: Migrate to TypeScript (#7809, #7972)[jest-haste-map] Optimize haste map tracking of deleted files with Watchman. (#8056)Readme
Stringify any JavaScript value.
JSON.stringify and significantly faster than Node's util.format)ReactTestComponent)$ npm install pretty-format
var prettyFormat = require('pretty-format');
var obj = { property: {} };
obj.circularReference = obj;
obj[Symbol('foo')] = 'foo';
obj.map = new Map();
obj.map.set('prop', 'value');
obj.array = [1, NaN, Infinity];
console.log(prettyFormat(obj));
Result:
Object {
"property": Object {},
"circularReference": [Circular],
"map": Map {
"prop" => "value"
},
"array": Array [
1,
NaN,
Infinity
],
Symbol(foo): "foo"
}
Object, Array, ArrayBuffer, DataView, Float32Array, Float64Array, Int8Array, Int16Array, Int32Array, Uint8Array, Uint8ClampedArray, Uint16Array, Uint32Array, arguments, Boolean, Date, Error, Function, Infinity, Map, NaN, null, Number, RegExp, Set, String, Symbol, undefined, WeakMap, WeakSet
Pretty format also supports adding plugins:
var fooPlugin = {
test: function(val) {
return val && val.hasOwnProperty('foo');
},
print: function(val, print, indent) {
return 'Foo: ' + print(val.foo);
}
};
var obj = { foo: { bar: {} } };
prettyFormat(obj, {
plugins: [fooPlugin]
});
// Foo: Object {
// "bar": Object {}
// }
ReactTestComponent and ReactElement pluginsvar prettyFormat = require('pretty-format');
var reactTestPlugin = require('pretty-format/plugins/ReactTestComponent');
var reactElementPlugin = require('pretty-format/plugins/ReactElement');
var React = require('react');
var renderer = require('react/lib/ReactTestRenderer');
var jsx = React.createElement('h1', null, 'Hello World');
prettyFormat(renderer.create(jsx).toJSON(), {
plugins: [reactTestPlugin, reactElementPlugin]
});
// <h1>
// Hello World
// </h1>
FAQs
Stringify any JavaScript value.
The npm package pretty-format receives a total of 66,809,111 weekly downloads. As such, pretty-format popularity was classified as popular.
We found that pretty-format demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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