babel-plugin-debug-macros

What is babel-plugin-debug-macros?

The babel-plugin-debug-macros package is a Babel plugin that allows you to conditionally include or exclude code based on compile-time flags. This is particularly useful for debugging, logging, and feature flagging in JavaScript applications.

What are babel-plugin-debug-macros's main functionalities?

Conditional Code Inclusion

This feature allows you to include or exclude code based on a compile-time flag. In this example, the console.log statement will only be included if the DEBUG flag is set to true.

const DEBUG = true;
if (DEBUG) {
  console.log('Debugging is enabled');
}

Feature Flagging

This feature allows you to enable or disable features based on environment variables. In this example, the console.log statement will only be included if the FEATURE_X_ENABLED environment variable is set to 'true'.

const FEATURE_X_ENABLED = process.env.FEATURE_X_ENABLED === 'true';
if (FEATURE_X_ENABLED) {
  console.log('Feature X is enabled');
}

Debugging

This feature allows you to include debugging code that will only be included in non-production environments. In this example, the console.log statement will only be included if the NODE_ENV environment variable is not set to 'production'.

const DEBUG = process.env.NODE_ENV !== 'production';
if (DEBUG) {
  console.log('This is a debug message');
}

Other packages similar to babel-plugin-debug-macros

babel-plugin-transform-inline-environment-variables

This package allows you to inline environment variables into your code at compile time. It is similar to babel-plugin-debug-macros in that it allows you to conditionally include or exclude code based on environment variables, but it does not provide the same level of flexibility for feature flagging and debugging.

babel-plugin-preval

This package allows you to evaluate code at build time and inline the result into your code. It is similar to babel-plugin-debug-macros in that it allows you to include or exclude code based on compile-time conditions, but it is more focused on inlining the results of computations rather than conditional code inclusion.

babel-plugin-conditional-compile

This package allows you to conditionally include or exclude code based on compile-time flags. It is very similar to babel-plugin-debug-macros, but it is less focused on debugging and more focused on general-purpose conditional code inclusion.

README

Babel Debug Macros And Feature Flags

This provides debug macros and feature flagging.

Setup

The plugin takes 4 types options: flags, svelte, debugTools, and externalizeHelpers. The importSpecifier is used as a hint to this plugin as to where macros are being imported and completely configurable by the host.

Like Babel you can supply your own helpers using the externalizeHelpers options.

{
  plugins: [
    ['babel-plugin-debug-macros', {
      // @optional
      debugTools: {
        isDebug: true,
        source: 'debug-tools',
        // @optional
        assertPredicateIndex: 0
      },

      flags: [
        { source: '@ember/env-flags', flags: { DEBUG: true } },
        {
          name: 'ember-source',
          source: '@ember/features',
          flags: {
            FEATURE_A: false,
            FEATURE_B: true,
            DEPRECATED_CONTROLLERS: "2.12.0"
          }
        }
      ],

      // @optional
      svelte: {
        'ember-source': "2.15.0"
      },

      // @optional
      externalizeHelpers: {
        module: true,
        // global: '__my_global_ns__'
      }
    }]
  ]
}

Flags and features are inlined into the consuming module so that something like UglifyJS will DCE them when they are unreachable.

Simple environment and feature flags

import { DEBUG } from '@ember/env-flags';
import { FEATURE_A, FEATURE_B } from '@ember/features';

if (DEBUG) {
  console.log('Hello from debug');
}

let woot;
if (FEATURE_A) {
  woot = () => 'woot';
} else if (FEATURE_B) {
  woot = () => 'toow';
}

woot();

Transforms to:

if (true /* DEBUG */) {
  console.log('Hello from debug');
}

let woot;
if (false /* FEATURE_A */) {
  woot = () => 'woot';
} else if (true) {
  woot = () => 'toow';
}

woot();

warn macro expansion

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && console.warn('this is a warning'));

assert macro expansion

The assert macro can expand in a more intelligent way with the correct configuration. When babel-plugin-debug-macros is provided with the assertPredicateIndex the predicate is injected in front of the assertion in order to avoid costly assertion message generation when not needed.

import { assert } from 'debug-tools';

assert((() => {
  return 1 === 1;
})(), 'You bad!');

With the debugTools: { assertPredicateIndex: 0 } configuration the following expansion is done:

(true && !((() => { return 1 === 1;})()) && console.assert(false, 'this is a warning'));

When assertPredicateIndex is not specified, the following expansion is done:

(true && console.assert((() => { return 1 === 1;})(), 'this is a warning'));

deprecate macro expansion

import { deprecate } from 'debug-tools';

let foo = 2;

deprecate('This is deprecated.', foo % 2);

Expands into:

let foo = 2;

(true && !(foo % 2) && console.warn('This is deprecated.'));

Externalized Helpers

When you externalize helpers you must provide runtime implementations for the above macros. An expansion will still occur, however we will emit references to those runtime helpers.

A global expansion looks like the following:

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && Ember.warn('this is a warning'));

While externalizing the helpers to a module looks like the following:

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && warn('this is a warning'));

Svelte

Svelte allows for consumers to opt into stripping deprecated code from your dependecies. By adding a package name and minimum version that contains no deprecations, that code will be compiled away.

For example, consider you are on ember-source@2.10.0 and you have no deprecations. All deprecated code in ember-source that is <=2.10.0 will be removed.

svelte: {
  "ember-source": "2.10.0"
}

Now if you bump to ember-source@2.11.0 you may encounter new deprecations. The workflow would then be to clear out all deprecations and then bump the version in the svelte options.

svelte: {
  "ember-source": "2.11.0"
}