DefinePlugin

TheDefinePlugin replaces variables in your code with other values or expressions atcompile time. This can be useful for allowing different behavior between development builds and production builds. If you perform logging in your development build but not in the production build you might use a global constant to determine whether logging takes place. That's whereDefinePlugin shines, set it and forget it rules for development and production builds.

newwebpack.DefinePlugin({// Definitions...});

Usage

Each key passed intoDefinePlugin is an identifier or multiple identifiers joined with..

If the value is a string it will be used as a code fragment.
If the value isn't a string, it will be stringified (including functions).
If the value is an object all keys are defined the same way.
If you prefixtypeof to the key, it's only defined for typeof calls.

The values will be inlined into the code allowing a minification pass to remove the redundant conditional.

newwebpack.DefinePlugin({PRODUCTION:JSON.stringify(true),VERSION:JSON.stringify('5fa3b9'),BROWSER_SUPPORTS_HTML5:true,TWO:'1+1','typeof window':JSON.stringify('object'),'process.env.NODE_ENV':JSON.stringify(process.env.NODE_ENV),});

console.log('Running App version '+VERSION);if(!BROWSER_SUPPORTS_HTML5)require('html5shiv');

warning

When defining values forprocess prefer'process.env.NODE_ENV': JSON.stringify('production') overprocess: { env: { NODE_ENV: JSON.stringify('production') } }. Using the latter will overwrite theprocess object which can break compatibility with some modules that expect other values on the process object to be defined.

tip

Note that because the plugin does a direct text replacement, the value given to it must includeactual quotes inside of the string itself. Typically, this is done either with alternate quotes, such as'"production"', or by usingJSON.stringify('production').

if(!PRODUCTION){  console.log('Debug info');}if(PRODUCTION){  console.log('Production log');}

After passing through webpack with no minification results in:

if(!true){  console.log('Debug info');}if(true){  console.log('Production log');}

and then after a minification pass results in:

console.log('Production log');

Feature Flags

Enable/disable features in production/development build usingfeature flags.

newwebpack.DefinePlugin({NICE_FEATURE:JSON.stringify(true),EXPERIMENTAL_FEATURE:JSON.stringify(false),});

Service URLs

Use a different service URL in production/development builds:

newwebpack.DefinePlugin({SERVICE_URL:JSON.stringify('https://dev.example.com'),});

Runtime values via`runtimeValue`

function (getterFunction, [string] | true | object) => getterFunction()

It is possible to define variables with values that rely on files and will be re-evaluated when such files change in the file system. This means webpack will rebuild when such watched files change.

There're two arguments forwebpack.DefinePlugin.runtimeValue function:

The first argument is afunction(module, key, version) that should return the value to be assigned to the definition.
The second argument could either be an array of file paths to watch for or atrue to flag the module as uncacheable. Since 5.26.0, it can also take an object argument with the following properties:
- fileDependencies?: string[] A list of files the function depends on.
- contextDependencies?: string[] A list of directories the function depends on.
- missingDependencies?: string[] A list of not existing files the function depends on.
- buildDependencies?: string[] A list of build dependencies the function depends on.
- version?: string | () => string A version of the function.

const fileDep= path.resolve(__dirname,'sample.txt');newwebpack.DefinePlugin({BUILT_AT: webpack.DefinePlugin.runtimeValue(Date.now,{    fileDependencies:[fileDep],}),});