Performance

This page describes a few topics around Knip’s performance, and how you might improve it.

Knip does not want to tell you how to structure files or how to write your code, but it might still be good to understand inefficient patterns for Knip.

Star Imports and Barrel Files

Knip builds up a simplified graph of imports and exports and can quickly match them against each other to find unused exports. However, there might not be a literal match for exports that are imported using the import * syntax. In this case, Knip will ask the TypeScript compiler to find references, which is a lot more work. More levels of re-exports and star imports are more expensive.

Barrel files with re-exports look like this:

export * from './model';
export * from './util';

Example of a star import:

import * as MyNamespace from './helpers';

Use the --performance flag to see how often findReferences is used and how much time is spent there.

This article explains the issue in more detail: Speeding up the JavaScript ecosystem - The barrel file debacle. The conclusion: “Get rid of all barrel files”.

Workspace Sharing

Knip shares files from separate workspaces if the configuration in tsconfig.json allows this. This reduces memory consumption and run duration. The relevant compiler options are baseUrl and paths, and a workspace is shared if the following is true:

• The compilerOptions.baseUrl is not set explicitly
• There are no conflicting keys in compilerOptions.paths

With the --debug flag you can see how many programs Knip uses. Look for messages like this:

...
[*] Installed 2 programs for 29 workspaces
...
[*] Analyzing used resolved files [P1/1] (123)
...
[*] Analyzing used resolved files [P1/2] (8)
...
[*] Analyzing used resolved files [P2/1] (41)
...

The first number in P1/1 is the number of the program, the second number indicates additional entry files were found in the previous round so it does another round of analysis on those files.

findReferences

The findReferences function (from the TypeScript Language Service) is invoked for exported class members. If finding unused class members is enabled, use the --performance flag to see how many times this function is invoked and how much time is spent there:

knip --include classMembers --performance

The first invocation (per program) is especially expensive, as TypeScript sets up symbols and caching.

A Last Resort

In case Knip is unbearable slow (or even crashes), you could resort to lint individual workspaces.