JavaScript / TypeScript : Standard way to keep the cause of an Error

user_8584526 0
Viewed 6489

I have a background of Java developer and I'm quite new to JavaScript/TypeScript.

Is there a standard way to manage and keep the cause of an Error in JavaScript/TypeScript?

My purpose is to get a complete stacktrace when I wrap an Error into another ; a little bit as with Java Exception stacktrace:

Message of exception 1
...
Caused by: Message of exception 2
...
Caused by: Message of the root exception

I try this code but err1 doesn't keep the reference of err2:

// CODE
try {
    try {
        throw new Error("Error no2");
    } catch (err2) {
        console.log("========================================");
        console.log(err2);
        throw new Error("Error no1");
    }
} catch (err1) {
    console.log("========================================");
    console.log(err1);
}

// CONSOLE OUTPUT
$ node test.ts 
========================================
Error: Error no2
    at Object.<anonymous> (/tmp/test.ts:3:15)
    at Module._compile (internal/modules/cjs/loader.js:956:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:973:10)
    at Module.load (internal/modules/cjs/loader.js:812:32)
    at Function.Module._load (internal/modules/cjs/loader.js:724:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1025:10)
    at internal/main/run_main_module.js:17:11
========================================
Error: Error no1
    at Object.<anonymous> (/tmp/test.ts:7:15)
    at Module._compile (internal/modules/cjs/loader.js:956:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:973:10)
    at Module.load (internal/modules/cjs/loader.js:812:32)
    at Function.Module._load (internal/modules/cjs/loader.js:724:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1025:10)
    at internal/main/run_main_module.js:17:11

Besides, I don't find any property that is named cause in Error class. There is a stack property but I think it's a bad practice to change it.

Thanks!

typescript error-handling stack-trace javascript
2 Answers

2021 answer: There is now a standard way of managing and keeping the cause an error. The Error() constructor can now accept an options object as a second argument. This options object should have a cause property which would typically be another Error but it doesn't have to be.

Example

throw new Error('Outer Error', {cause: new Error('Inner Error')});

Support

At the time of writing (October 2021) there's support for the new constructor in Firefox, Chrome and Safari. To get the cause of an Error you'll need to interrogate it's cause property. Additionally in Firefox we get a bit of extra info in the console, e.g

Uncaught Error: Outer Error
    <anonymous> debugger eval code:1
Caused by: Error: Inner Error
    <anonymous> debugger eval code:1

Edge will currently just ignore the second constructor property.

Sources

Mozilla doc: https://developer.mozilla.org/en-US/docs/web/javascript/reference/global_objects/error

ECMAScript proposal: https://github.com/tc39/proposal-error-cause

user_19168160

I've always used a modification of Kristian's answer here

class TraceableError extends Error {
  trace: Error;

  constructor(message?: string, innerError?: Error) {
    super(message); 
    this.trace = innerError;

    const actualProto = new.target.prototype;

    if (Object.setPrototypeOf) { Object.setPrototypeOf(this, actualProto); } 
    else { this.__proto__ = actualProto; } 
  }
}

Then you would throw like this

try {
    try {
        throw new Error("Error no2");
    } catch (err2) {
        console.log("========================================");
        console.log(err2);
        throw new TraceableError ("Error no1", err2);
    }
} catch (err1) {
    console.log("========================================");
    console.log(err1);
}

Note that, if not caught, the trace part of the new error will not be output to the console.

user_14206140
Related