babel-plugin-log-deprecated

babel-plugin-log-deprecated

Adds a console.warn statement to the functions annotated with the JSDoc @deprecated tag.

The console.warn is added at the beginning of the function body.

• Example transpilation
• Motivation
• Using in production
• Implementation
  • Deprecation message fields
  • package.json resolution

Example transpilation

Input:

/**
 * @deprecated Deprecated in favour of quux.
 */
function foo () {
  bar();
};

Output:

/**
 * @deprecated Deprecated in favour of quux.
 */
function foo () {
  console.warn("Deprecated: Function \"foo\" is deprecated in /fixtures/preset-options/adds-console-warn-to-function-declaration/actual.js on line 4", {
    functionName: "foo",
    message: "Deprecated in favour of quux.",
    packageName: "bar",
    packageVersion: "1.0.0",
    scriptColumn: 0,
    scriptLine: 4,
    scriptPath: "fixtures/preset-options/adds-console-warn-to-function-declaration/actual.js"
  });

  bar();
};

Motivation

Working on a code base that has a large public API surface requires a method to instruct the consumer about deprecation of methods. The most common approach at the moment is to add an ad-hoc console.warn statement used to warn the consumer. There are multiple problems with this approach:

• It duplicates the role of the JSDoc @deprecated tag.
• It restricts the developer to the amount of the information that can be included in the deprecation message.
• It leads to a proliferation of arbitrary format console.log messages that can be hard to filter out.

To address these issues, babel-plugin-log-deprecated:

• Uses JSDoc @deprecated tag to construct the deprecation log message property.
• Utilises build time information (package.json configuration, script path) to enrich the deprecation message.
• Enforces a consistent error message format.

Using in production

This transpiler can be used to produce code for client-side use and Node.js. Whether to leave the warnings in the production build depends on the use case.

Regarding the client-side use, I have been asked:

inu-no-policemen:

Wouldn't it make more sense to get these messages at compile time?

Messages which only appear if a particular path is taken through the application are easy to miss.

– https://www.reddit.com/r/javascript/comments/5f71la/i_have_written_a_babel_transpiler_that_adds/dai062z/

I am using this plugin to add warning messages that are visible at a runtime on purpose. Think about large organizations that have multiple teams working on a frontend of the same website. There is a lot of code in the window namespace:

Website	Object.keys(window).length
https://www.google.com/blank.html	181 (base figure)
https://www.ft.com/	229 (+48)
https://www.theguardian.com/uk	269 (+88)
http://www.dailymail.co.uk/home/index.html	599 (+418)
http://time.com/	669 (+488)

Furthermore, this is just the count of the properties in the window namespace. A number of these properties will expose complex APIs that tie together the entire website (think user targeting, advertising, utilities, etc.).

You cannot simply remove properties because you risk of breaking things. Therefore, a sensible solution is to communicate the upcoming changes to the other teams and add deprecation warnings well ahead of making the change.

In a similar fashion, a public library can use the deprecation warning to inform the consumers of the upcoming changes.

Implementation

Deprecation message fields

Name	Value
functionName	Name of the function that has the @deprecated tag associated with. In case of an anonymous function - name of the left hand side identifier.
message	Message provided in the description of the JSDoc @deprecated tag
packageName	Value of the name property in the package.json. See package.json resolution.
packageVersion	Value of the version property in the package.json. See package.json resolution.
scriptColumn	Number of the column where the function is declared.
scriptLine	Number of the line where the function is declared.
scriptPath	Path to the script file relative to package.json. See package.json resolution.

package.json resolution

package.json is resolved relative to the file being transpiled.