Proposal: Error.captureStackTrace

Daniel Minor @ Mozilla

Motivation

From MDN: The Error.captureStackTrace() static method installs stack trace information on a provided object as the stack property.

​

History

• In the depths of time, Chrome shipped Error.captureStackTrace (There’s evidence of it as early as 2015)
• In August 2023, JSC also shipped this method
• In March 2024, SpiderMonkey shipped this method as well, because of web compatibility problems.
• This proposal reached Stage 1 in February 2025

Work in Stage 1

Because browsers have already shipped, the design space is very small

Feedback from committee last time:

• Strong preference to install a property rather than an accessor
• No special behaviour for objects with an [[ErrorData]] slot

Investigated requiring the optional `constructor` argument to be callable:

• Telemetry showed about 0.8% of calls would be broken, doesn’t seem worth the risk

Proposed Specification

Issue #8: Causes observable changes with prepareStackTrace

• `prepareStackTrace` is a non-standard V8 API that allows custom formatting of the stack
• Currently, V8’s implementation uses a getter and lazily computes the stack, so `prepareStackTrace` isn’t called unless needed
• As specified, using a property would cause this to be computed eagerly, which could be expensive and change observable ordering, depending on what `prepareStackTrace` does

Consensus for

Stage 2?

Source: https://en.wikipedia.org/wiki/File:River_terrapin.jpg