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
jest 18.1.0
context variable.-h as alias for --help.Readme
Stringify any JavaScript value.
JSON.stringify and significantly faster than Node's util.format)ReactTestComponent)$ yarn add pretty-format
const 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
console.log(prettyFormat(object));
console.log(prettyFormat(object, options));
Options:
callToJSONboolean, default: truetoJSON() on passed object.indentnumber, default: 2maxDepthnumber, default: Infinityminboolean, default: falsepluginsarray, default: []printFunctionNameboolean, default: true[Function].escapeRegexboolean, default: falsehighlightboolean, default: falseReactTestComponent and ReactElement plugins.themeobject, default: {tag: 'cyan', content: 'reset'...}reset for no color.tag, content, prop and value.Pretty format also supports adding plugins:
const fooPlugin = {
test(val) {
return val && val.hasOwnProperty('foo');
},
print(val, print, indent) {
return 'Foo: ' + print(val.foo);
}
};
const obj = {foo: {bar: {}}};
prettyFormat(obj, {
plugins: [fooPlugin]
});
// Foo: Object {
// "bar": Object {}
// }
ReactTestComponent and ReactElement pluginsconst prettyFormat = require('pretty-format');
const reactTestPlugin = require('pretty-format/build/plugins/ReactTestComponent');
const reactElementPlugin = require('pretty-format/build/plugins/ReactElement');
const React = require('react');
const renderer = require('react-test-renderer');
const element = React.createElement('h1', null, 'Hello World');
prettyFormat(renderer.create(element).toJSON(), {
plugins: [reactTestPlugin, reactElementPlugin]
});
// <h1>
// Hello World
// </h1>
FAQs
Stringify any JavaScript value.
The npm package pretty-format receives a total of 66,752,880 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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