feat: add JsFunction value type for composable executeJs#24374
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Lets server code build a JS function value with captured parameters and pass it as an executeJs parameter, removing the need to string-concatenate framework boilerplate around user-supplied JS. Captures may themselves be Elements or other JsFunctions; the codec encodes them recursively as @v-fn, and the client reifies the value as a callable function with the captures pre-bound.
Adds JsFunction.withArguments(String...) so the materialised function accepts caller-supplied arguments at invocation time, in addition to the pre-bound captures. The wire format gains an "args" field listing the parameter names, which the client passes through to new Function after the capture slots. Closes #24373
Legioth
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May 19, 2026
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There's no test that verifies that this works end-to-end. There are also no tests for the client-side functionality, but it might be enough with the end-to-end test without any dedicated client-side tests.
Client-side, switch from Function.prototype.bind to a wrapper that applies captures while letting the caller control this. The previous .bind implementation also bound this to undefined, so callers could not later set it via .call() or .apply() — which breaks the intended "$0.call(element)" composition pattern from the design discussion. JsFunction: drop the redundant constructor-side defensive copies (the of() factory already clones, and withArguments() now uses List.of() so the constructor can trust both lists). argumentNames defaults to Collections.emptyList(), avoiding a fresh String[0] per instance. Document JsFunction support alongside the existing Element and BaseJsonNode special cases in Element.executeJs and Page.executeJs. Add JsFunctionView + JsFunctionIT exercising captures-only, named runtime arguments, Element captures, and caller-supplied this so the binding fix is verified end-to-end.
Legioth
requested changes
May 19, 2026
Throw IllegalStateException if withArguments is called on a JsFunction that already has argument names. Silent overwrite would hide a mistake where two callers each thought they owned the parameter list.
Legioth
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May 19, 2026
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Lets server code build a JS function value with captured parameters
and pass it as an executeJs parameter, removing the need to
string-concatenate framework boilerplate around user-supplied JS.
Captures may themselves be Elements or other JsFunctions; the codec
encodes them recursively as @v-fn, and the client reifies the value
as a callable function with the captures pre-bound.
Fixes #24373