webpack "Critical dependency: the request of a dependency is an expression"

webpack found a require() whose argument is a runtime expression, not a static string, so it cannot know which module to bundle. It emits "Critical dependency" - harmless as a warning, but CI configured to fail on warnings turns it into a build failure.

What this error means

The build prints Critical dependency: the request of a dependency is an expression, pointing at a package (often express, a logger, or an ORM) that builds a require path dynamically. With --bail or warning-as-error CI, the build then fails.

webpack

WARNING in ./node_modules/express/lib/view.js 81:13-25
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/express/lib/application.js
 @ ./src/server.js

Common causes

Dynamic require in a dependency

A library uses require(variable) or require(./${name}). webpack cannot statically resolve it, so it warns that the request is an expression.

CI treats warnings as failures

A stats.warningsFilter-less build with --bail, or a CI step that greps for "WARNING", elevates the otherwise-benign message into a hard failure.

How to fix it

Suppress the known-benign warning

When the dynamic require is in a server-side dependency you do not actually bundle for the browser, mark it external or ignore it.

webpack.config.js

// webpack.config.js
module: {
  // exprContextCritical: false  // silences expression-context warnings
},
ignoreWarnings: [/the request of a dependency is an expression/],

Externalize the offending package

For Node targets, add the package to externals so webpack does not try to bundle its dynamic requires.
Set target: 'node' for server bundles so built-in/dynamic modules are left to the runtime.
Do not fail CI on this specific warning if the dependency is intentionally dynamic.

How to prevent it

Set target: 'node' and use externals for server-side bundles.
Scope CI warning-as-error gates so known-benign dynamic-require warnings do not fail the build.
Avoid dynamic require(expr) in your own code; use static imports.