Jest测试报错TypeError: Line_vue_1.default不是构造函数求助

Let's break down why this error is happening and how to fix it, based on your setup:

Root Cause #

When testing a class that inherits from your custom LineBase (which extends Vue), Jest's module resolution or transpilation isn't correctly resolving the default export of your Line class. Your console.log(typeof Line) returning object confirms this—you're getting the module wrapper object instead of the actual constructor function.

Solutions to Try #

1. Sync esModuleInterop Between TSConfig and Jest #

Your tsconfig.json has esModuleInterop: true, but Jest might not be inheriting this setting. Add it to your Jest config to ensure consistent module handling:

Update your jest.config.js:

module.exports = {
  // ... existing config
  globals: {
    "ts-jest": {
      esModuleInterop: true,
      tsconfig: "./tsconfig.json" // Explicitly align with your TS config
    }
  },
  // ... rest of config
};

2. Adjust Import Syntax in Tests #

If the above doesn't resolve the issue, your transpiled code might be wrapping the default export in a module object. Try accessing the constructor directly from the module:

// Replace this:
import Line from '@/path/to/Line';

// With this:
import * as LineModule from '@/path/to/Line';
const Line = LineModule.default;

const instance = new Line(); // This should now work

3. Mirror Vue Alias in Jest #

Your vue.config.js aliases vue to a specific node_modules path to avoid duplicate Vue instances. Mirror this in Jest to prevent context mismatches:

Add to your jest.config.js moduleNameMapper:

moduleNameMapper: {
  ...pathsToModuleNameMapper(compilerOptions.paths),
  "^vue$": "<rootDir>/node_modules/vue" // Match your app's Vue alias
},

4. Verify Class File Setup #

Double-check these details:

• Ensure LineBase and Line are saved as .ts files (not .vue single-file components)—your Jest transform for .vue files is meant for SFCs, not plain class files.
• Confirm no conflicting exports exist in either class file (your code shows correct default exports, but typos can slip in).

5. Ensure Your Source Files Are Transpiled #

Add your app's source directory to Jest's excluded ignore list to make sure your classes are transpiled:

Update transformIgnorePatterns in jest.config.js:

transformIgnorePatterns: [
  "node_modules/(?!variables/.*)",
  "<rootDir>/node_modules/button-plugin-vue",
  "!ClientApp/**/*" // Don't ignore your app's source files
],

Test After Changes #

After applying one or more of these fixes, re-run your Jest test. The new Line() call should now correctly instantiate your class without the constructor error.

内容的提问来源于stack exchange，提问作者Ulia Savi