{"record":{"id":"7704357dbcf22150","repo":"angular/angular-cli","slug":"terser-failed-for-unknown-reason","errorCode":null,"errorMessage":"Terser failed for unknown reason.","messagePattern":"Terser failed for unknown reason\\.","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"packages/angular_devkit/build_angular/src/tools/webpack/plugins/javascript-optimizer-worker.ts","lineNumber":229,"sourceCode":"      // esbuild in the first pass is used to minify function names\n      keep_fnames: true,\n      format: {\n        // ASCII output is enabled here as well to prevent terser from converting back to UTF-8\n        ascii_only: true,\n        wrap_func_args: false,\n      },\n      sourceMap:\n        sourcemaps &&\n        ({\n          asObject: true,\n          // typings don't include asObject option\n          // eslint-disable-next-line @typescript-eslint/no-explicit-any\n        } as any),\n    },\n  );\n\n  if (typeof result.code !== 'string') {\n    throw new Error('Terser failed for unknown reason.');\n  }\n\n  return { code: result.code, map: result.map as object };\n}\n\n/**\n * Determines if an unknown value is an esbuild BuildFailure error object thrown by esbuild.\n * @param value A potential esbuild BuildFailure error object.\n * @returns `true` if the object is determined to be a BuildFailure object; otherwise, `false`.\n */\nfunction isEsBuildFailure(value: unknown): value is BuildFailure {\n  return !!value && typeof value === 'object' && 'errors' in value && 'warnings' in value;\n}\n","sourceCodeStart":211,"sourceCodeEnd":243,"githubUrl":"https://github.com/angular/angular-cli/blob/bb72145f9ab45aee29f523236b3a25cd0813a841/packages/angular_devkit/build_angular/src/tools/webpack/plugins/javascript-optimizer-worker.ts#L211-L243","documentation":"optimizeWithTerser calls the Terser API (via the worker pool) and expects result.code to be a string. When Terser returns a non-string code — typically because minification failed and it returned an error object/undefined instead — this error is thrown as a fallback because Terser did not surface a specific message. It means the Terser minification step failed without a diagnosable reason.","triggerScenarios":"Running the JavaScriptOptimizerWorker's optimizeWithTerser on a file whose Terser invocation returns { code: undefined } — e.g. invalid or exotic ES syntax Terser cannot parse, or a Terser internal error swallowed by the worker.","commonSituations":"Bundling code with syntax unsupported by the configured Terser/ECMA target; oversized or malformed generated bundles; incompatibility between the terser version resolved and the one expected by build-angular after dependency drift.","solutions":["Set optimization to false temporarily (angular.json: configurations.production.optimization=false) to confirm Terser is the failing step, then narrow down the offending chunk","Check the bundle for syntax Terser cannot handle and transpile it earlier (adjust target/compilerOptions.target in tsconfig to a lower ES level)","Pin/align the terser version with what @angular-devkit/build-angular expects (npm ls terser) and reinstall to fix hoisting mismatches","Upgrade @angular-devkit/build-angular / Angular CLI to the latest patch to pick up Terser fixes"],"exampleFix":"// before (tsconfig.json)\n{\"compilerOptions\": {\"target\": \"ESNext\"}}\n// after\n{\"compilerOptions\": {\"target\": \"ES2020\"}}","handlingStrategy":"try-catch","validationCode":"if (typeof input !== 'string' || input.length === 0) {\n  throw new Error('invalid input passed to terser optimizer');\n}","typeGuard":"function isTerserResult(r: unknown): r is { code: string; map?: object } {\n  return typeof r === 'object' && r !== null && typeof (r as any).code === 'string';\n}","tryCatchPattern":"try {\n  const out = await optimizeWithTerser(/* ... */);\n} catch (err) {\n  if (err.message === 'Terser failed for unknown reason.') {\n    logger.warn(`terser failed for ${file}; keeping unminified output`);\n    return { code: originalCode, map: undefined };\n  }\n  throw err;\n}","preventionTips":["Keep tsconfig target within what Terser supports","Pin the terser version alongside build-angular","Test minification in CI so regressions surface early","Temporarily disable optimization to isolate failing chunks"],"tags":["terser","minification","webpack","angular-cli"],"backgroundTag":"terser-minification-failed","analyzedSha":"bb72145f9ab45aee29f523236b3a25cd0813a841","analyzedAt":"2026-08-30T02:47:34.745Z","schemaVersion":2},"datasetVersion":"2026-08-30T03:17:51.788Z"}