Is there any harm in updating the message of an Error object like this?
const err = new Error('bar');
...
err.message = `foo ${err.message}`;
My objective is to add some useful information to the error message when logging the error.
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2 Answers
It can be useful to add some extra information/breadcrumbs as an exception travels up through your application layers. That said, you are mutating an object, which can be hard to reason about in a large code-base; exceptions management normally being a cross-cutting concern in your application.
Also bear in mind that some libraries will extend the Error class and leave the message property without a setter, making it ready-only.
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I just noticed some harm :-(
On chrome 127.0.6533.17 (but not firefox 127.0.2), after your code, the error object is in a screwy state, in which err.message contains your additional annotation, but printing err does not show it:
const err = new Error('bar');
err.message = `foo ${err.message}`;
console.log("err.message = ",err.message); // "err.message = foo bar"
console.log("err = ",err); // "err =\nError: bar\n at <anonymous>:1:13"
The above is from chrome. On firefox, it shows "foo bar" in the final message instead.
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