Typescript is not identifying Instance of subclass of Error?

Question

I have the following code:

export class PutTimeEntryValidationError extends Error {
  constructor(message: string, public errors: PutTimeEntryError[]) {
    super(message);
  }
}

try {
   throw new PutTimeEntryValidationError("test",[]);
} catch(ex){
   if (ex instanceof PutTimeEntryValidationError){
      debugger; // 
   } else {
      debugger; // code stops here somehow
   } 
}

Im using webpack 3 with awesome typescript loader and this tsconfig.js:

{
    "compilerOptions": {
        "outDir": "./wwwroot/js/", // path to output directory
        "sourceMap": true, // allow sourcemap support
        "noImplicitAny": false, 
        "strictNullChecks": true, // enable strict null checks as a best practice
        "module": "commonjs", // specifiy module code generation
        "jsx": "react",             // use typescript to transpile jsx to js
        "target": "es5", // specify ECMAScript target version
        "allowJs": true, // allow a partial TypeScript and JavaScript codebase
        "emitDecoratorMetadata": true,
        "experimentalDecorators": true,
        "lib": [
            "es2015", 
            "es5", //needed for hmr
            "es6",
            "dom"
        ],
        "noUnusedLocals": false
    },
    "include": [
        "./react/**/*"
    ]
}

and:

  "typescript": "^2.4.1",

how come my error is not actually a subclass of Error?

// _1 is compiled suffix
ex_1 instanceof Error //true
ex_1.__proto__ // name: Error

Sorry i was to quickly, this is a duplicate: stackoverflow.com/a/41102306/1275832 — Joel Harkes
– Joel Harkes, Commented Mar 8, 2018 at 14:32

Joel Harkes · Accepted Answer · 2018-03-08 14:47:41Z

1

For those coming here.

I fond this was the solution:

export class PutTimeEntryValidationError extends Error {
    constructor(message: string, public errors: PutTimeEntryError[]) {
        super(message);

        // Fix prototype:
        Object.setPrototypeOf(this, PutTimeEntryValidationError.prototype);
    }
}

apparently transpiling to es5 breaks this.

answered Mar 8, 2018 at 14:47

Joel Harkes

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