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hooks: Refine caveat comments about function parameter count

pull/4698/head
Richard Hansen 2021-01-31 16:15:52 -05:00 committed by John McLear
parent f02f288e80
commit c89db33ff0
1 changed files with 32 additions and 8 deletions
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40
src/static/js/pluginfw/hooks.js
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@ -165,14 +165,27 @@ const callHookFnSync = (hook, context) => {
// The hook function is assumed to not have a callback parameter, so fall through and accept
// `undefined` as the resolved value.
//
// IMPORTANT: "Rest" parameters and default parameters are not counted in`Function.length`, so
// the assumption does not hold for wrappers like `(...args) => { real(...args); }`. Such
// functions will still work properly without any logged warnings or errors for now, but:
// IMPORTANT: "Rest" parameters and default parameters are not included in `Function.length`,
// so the assumption does not hold for wrappers such as:
//
// const wrapper = (...args) => real(...args);
//
// ECMAScript does not provide a way to determine whether a function has default or rest
// parameters, so there is no way to be certain that a hook function with `length` < 3 will
// not call the callback. Synchronous hook functions that call the callback even though
// `length` < 3 will still work properly without any logged warnings or errors, but:
//
// * Once the hook is upgraded to support asynchronous hook functions, calling the callback
// will (eventually) cause a double settle error, and the function might prematurely
// asynchronously will cause a double settle error, and the hook function will prematurely
// resolve to `undefined` instead of the desired value.
//
// * The above "unsettled function" warning is not logged if the function fails to call the
// callback like it is supposed to.
//
// Wrapper functions can avoid problems by setting the wrapper's `length` property to match
// the real function's `length` property:
//
// Object.defineProperty(wrapper, 'length', {value: real.length});
}
}
@ -300,10 +313,21 @@ const callHookFnAsync = async (hook, context) => {
// The hook function is assumed to not have a callback parameter, so fall through and accept
// `undefined` as the resolved value.
//
// IMPORTANT: "Rest" parameters and default parameters are not counted in `Function.length`,
// so the assumption does not hold for wrappers like `(...args) => { real(...args); }`. For
// such functions, calling the callback will (eventually) cause a double settle error, and
// the function might prematurely resolve to `undefined` instead of the desired value.
// IMPORTANT: "Rest" parameters and default parameters are not included in
// `Function.length`, so the assumption does not hold for wrappers such as:
//
// const wrapper = (...args) => real(...args);
//
// ECMAScript does not provide a way to determine whether a function has default or rest
// parameters, so there is no way to be certain that a hook function with `length` < 3 will
// not call the callback. Hook functions with `length` < 3 that call the callback
// asynchronously will cause a double settle error, and the hook function will prematurely
// resolve to `undefined` instead of the desired value.
//
// Wrapper functions can avoid problems by setting the wrapper's `length` property to match
// the real function's `length` property:
//
// Object.defineProperty(wrapper, 'length', {value: real.length});
}
}