writeFile

Write to a file with the specified contents.

Syntax

cy.writeFile(filePath, contents)
cy.writeFile(filePath, contents, encoding)
cy.writeFile(filePath, contents, options)
cy.writeFile(filePath, contents, encoding, options)

Usage

Correct Usage

cy.writeFile('menu.json')

Arguments

filePath (String)

A path to a file within the project root (the directory that contains the default cypress.json).

contents (String, Array, Object or Buffer)

The contents to be written to the file.

encoding (String)

The encoding to be used when writing to the file. The following encodings are supported:

• 'ascii'
• 'base64'
• 'binary'
• 'hex'
• 'latin1'
• 'utf8'
• 'utf-8'
• 'ucs2'
• 'ucs-2'
• 'utf16le'
• 'utf-16le'
• null

Using null explicitly will allows you to write a Buffer directly, without first encoding it as a string.

options (Object)

Pass in an options object to change the default behavior of cy.writeFile().

To use encoding with other options, have your options object be your third parameter and include encoding there. This is the same behavior as fs.writeFile.

Yields

• cy.writeFile() yields null.

Examples

Text

Write some text to a txt file

If the path to the file does not exist, the file and its path will be created. If the file already exists, it will be over-written.

cy.writeFile('path/to/message.txt', 'Hello World')
cy.readFile('path/to/message.txt').then((text) => {
  expect(text).to.equal('Hello World') // true
})

{projectRoot}/path/to/message.txt will be created with the following contents:

 "Hello World"

JSON

Write JSON to a file

JavaScript arrays and objects are stringified and formatted into text.

cy.writeFile('path/to/data.json', { name: 'Eliza', email: '[email protected]' })
cy.readFile('path/to/data.json').then((user) => {
  expect(user.name).to.equal('Eliza') // true
})

{projectRoot}/path/to/data.json will be created with the following contents:

{
  "name": "Eliza",
  "email": "[email protected]"
}

Write response data to a fixture file

cy.request('https://jsonplaceholder.typicode.com/users').then((response) => {
  cy.writeFile('cypress/fixtures/users.json', response.body)
})

// our fixture file is now generated and can be used
cy.fixture('users').then((users) => {
  expect(users[0].name).to.exist
})

Encoding

Specify the encoding as a String

cy.writeFile('path/to/ascii.txt', 'Hello World', 'ascii'))

{projectRoot}/path/to/message.txt will be created with the following contents:

Hello World

Specify the encoding as part of the options object

cy.writeFile('path/to/ascii.txt', 'Hello World', {
  encoding: 'ascii',
  flag: 'a+',
})

Flags

Append contents to the end of a file

cy.writeFile('path/to/message.txt', 'Hello World', { flag: 'a+' })

Note that appending assumes plain text file. If you want to merge a JSON object for example, you need to read it first, add new properties, then write the combined result back.

const filename = '/path/to/file.json'

cy.readFile(filename).then((obj) => {
  obj.id = '1234'
  // write the merged object
  cy.writeFile(filename, obj)
})

Similarly, if you need to push new items to an array

const filename = '/path/to/list.json'

cy.readFile(filename).then((list) => {
  list.push({ item: 'example' })
  // write the merged array
  cy.writeFile(filename, list)
})

Buffer

Write a buffer directly without encoding as a string

const filename = '/path/to/file.png'

cy.readFile(filename, null).then((obj) => {
  // <Buffer ef 3a bf ... >
  cy.writeFile(filename, obj, null)
})

Rules

Requirements

• cy.writeFile() requires being chained off of cy.
• cy.writeFile() requires the file be successfully written to disk. Anything preventing this such as OS permission issues will cause it to fail.

Assertions

• cy.writeFile() will only run assertions you have chained once, and will not retry.

Timeouts

• cy.writeFile() can time out when the content being written takes a significant amount of time to encode.

Command Log

Write an array to a file

cy.writeFile('info.log', ['foo', 'bar', 'baz'])

The command above will display in the Command Log as:

When clicking on the writeFile command within the command log, the console outputs the following:

History

See also

• cy.readFile()