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4.14.0

Jint 4.14.0 is an interop-focused performance release: CLR arrays now cross into script as live views instead of copies, recently wrapped host objects reuse their wrappers, single-candidate interop method calls dispatch through compiled invokers, and JSON.parse interns repeated keys and values. Host collection traversal is 10.9× faster than 4.13.0. Two interop defaults changed in this release — read the first two highlights if you pass CLR arrays to scripts or rely on per-crossing conversion behavior; everything else needs no code changes to benefit.

Highlights

CLR arrays are live views by default (behavior change). Options.Interop.ArrayConversion now defaults to ArrayConversionMode.LiveView (#​2721, #​2728, #​2735): a single-rank T[] crossing into script becomes a live, fixed-size view over the underlying array — the way wrapped List<T> already behaves — instead of being copied into a new JS array on every read. Writes go through in both directions, and arrays exposed through read-only-declared members (e.g. IReadOnlyList<T>) produce read-only views. Iteration, Array.prototype methods, JSON serialization, index-key enumeration (Object.keys / for..in yield "0".."n-1") and undefined for out-of-range reads all behave array-like, but Array.isArray returns false, and because CLR arrays are fixed-size, resizing operations (push/pop/length writes) throw a TypeError like integer-indexed exotic objects do — shift/splice may move elements before their length change throws, as for typed arrays. Set Options.Interop.ArrayConversion = ArrayConversionMode.Copy to restore the 4.13 behavior.

Recently wrapped CLR objects reuse their wrappers (behavior change). The new Options.Interop.CacheRecentObjectWrappers defaults to true (#​2734): a small bounded ring (8 entries, keyed by reference identity and exposed type) reuses wrappers for host objects that repeatedly cross into script. Wrapper identity becomes stable (host.Obj === host.Obj), script-attached state (freeze, defineProperty, expandos) survives crossings, and the per-crossing wrapper allocation disappears. Under Copy array conversion this also means repeated reads of the same CLR array reuse the first JsArray snapshot while it stays cached — CLR-side mutations are not re-copied; set the option to false for the pre-4.14 fresh-snapshot-per-crossing behavior. Engine.Dispose() releases the ring.

Interop fast lanes. Single-candidate method calls run through a compiled invoker that binds and invokes without argument arrays or boxing (#​2733), with per-parameter binding flags precomputed (#​2719). Resolved ObjectWrapper members get a per-call-site inline cache (#​2722) and the member-call fast path covers primitive string receivers (#​2717). Array-like wrapper creation is a cached factory call with lazily materialized length (#​2730), primitive elements convert without boxing on both indexed reads and Array.prototype iteration (#​2731, #​2735), the wrapper identity caches cover CLR arrays (#​2716), and implicitly implemented interface methods are deduplicated in member resolution (#​2711).

JSON. JSON.parse interns property keys and string values within a parse, parses numbers off the span with an exactly-rounded fast path and scans string content in bulk (#​2718, #​2725, #​2732) — the json-parse-modern comparison row is 6% faster with 23% less allocation than 4.13.0. Parsing is also aligned with the JSON grammar (#​2738): malformed numbers like -09 and 1. are now rejected as in V8, while raw U+2028/U+2029 in strings and escaped control characters in keys — both valid JSON — are now accepted.

Strings. Chained slice/substring and split segments stay zero-copy views (#​2720), whole-string substring/substr return the receiver, and mismatched-length comparisons no longer materialize views (#​2740).

Execution constraints at host boundaries. Timeouts and cancellation are re-checked when control returns from host CLR code, so detection latency is bounded by one host call instead of a statement-count window, without adding per-statement cost — gated on execution depth so host-side reads of wrapped objects on an idle engine never observe a stale timer (#​2713, #​2714, #​2715). Execution-context depth stays balanced when constraint exceptions unwind generator/async frames, and a host callback that re-enters the engine no longer resets the outer script's budget (#​2736).

Correctness (including a pre-release review). A review of everything since 4.13.0 fixed: spurious TDZ when a for-header reads a name the loop body shadows (#​2709) and stale closure captures from destructuring defaults in for-loop headers (#​2739); the compiled-invoker lane now defers to custom ITypeConverters and preserves reflection exception types (#​2737); and the new wrapper defaults were hardened — declared-type contracts for arrays (an IReadOnlyList<T>-typed member no longer yields a writable view), a static type-mapper poisoning crash, Engine.Dispose releasing the wrapper caches, and JS-array in/enumeration/out-of-range semantics on array views (#​2735). Closure reads memoize slot-cache chain reachability (#​2726).

On the engine comparison benchmarks, Jint 4.14.0 beats ClearScript (native V8) by 7.1×–9.1× on every script ↔ host interop row — host collection traversal went from last to second among all engines at 15,597 → 1,433 µs with 99% less allocation — while remaining the fastest managed engine on 10 of 12 pure-JS scripts and the fastest interpreter on all 12, and now leading array-stress and dromaeo-object-array, rows V8 narrowly led at 4.13.0.

What's Changed

• Refresh EngineComparison benchmarks for 4.13.0 by @​lahma in Refresh EngineComparison benchmarks for 4.13.0 sebastienros/jint#2704
• Fix spurious TDZ when a for-header reads a name the loop body shadows by @​svenrog in Fix spurious TDZ when a for-header reads a name the loop body shadows sebastienros/jint#2709
• Bump the testing group with 1 update by @​dependabot[bot] in Bump the testing group with 1 update sebastienros/jint#2710
• Add tests for using modules from script code run via Evaluate by @​lahma in Add tests for using modules from script code run via Evaluate sebastienros/jint#2712
• Deduplicate implicitly implemented interface methods in member resolution by @​lahma in Deduplicate implicitly implemented interface methods in member resolution sebastienros/jint#2711
• Re-check amortized constraints at interpreter/host-code boundaries by @​lahma in Re-check amortized constraints at interpreter/host-code boundaries sebastienros/jint#2713
• Add ClearScript V8 to engine comparison benchmarks, trim suite, add script-to-host interop suite by @​viceice in Add ClearScript V8 to engine comparison benchmarks, trim suite, add script-to-host interop suite sebastienros/jint#1775
• Gate host-boundary constraint checks on active evaluation and harden coverage by @​lahma in Gate host-boundary constraint checks on active evaluation and harden coverage sebastienros/jint#2714
• Key the host-boundary constraint gate on execution depth and close remaining lanes by @​lahma in Key the host-boundary constraint gate on execution depth and close remaining lanes sebastienros/jint#2715
• Cover CLR arrays with the interop identity caches by @​lahma in Cover CLR arrays with the interop identity caches sebastienros/jint#2716
• Extend the member-call fast path to primitive string receivers by @​lahma in Extend the member-call fast path to primitive string receivers sebastienros/jint#2717
• Intern object property keys within a single JSON parse by @​lahma in Intern object property keys within a single JSON parse sebastienros/jint#2718
• Precompute per-parameter interop binding flags by @​lahma in Precompute per-parameter interop binding flags sebastienros/jint#2719
• Keep slice-of-slice and split segments zero-copy by @​lahma in Keep slice-of-slice and split segments zero-copy sebastienros/jint#2720
• Add opt-in ClrArrayConversion.LiveView interop mode for CLR arrays by @​lahma in Add opt-in ClrArrayConversion.LiveView interop mode for CLR arrays sebastienros/jint#2721
• Cache resolved ObjectWrapper members per member-expression node by @​lahma in Cache resolved ObjectWrapper members per member-expression node sebastienros/jint#2722
• Refresh engine comparison README after the V8-gap campaign by @​lahma in Refresh engine comparison README after the V8-gap campaign sebastienros/jint#2723
• Bulk string scanning and a simple-number fast path for JSON.parse by @​lahma in Bulk string scanning and a simple-number fast path for JSON.parse sebastienros/jint#2725
• Memoize slot-cache chain reachability for closure reads by @​lahma in Memoize slot-cache chain reachability for closure reads sebastienros/jint#2726
• Refresh engine comparison tables after the second campaign round by @​lahma in Refresh engine comparison tables after the second campaign round sebastienros/jint#2727
• Default Interop.ArrayConversion to LiveView for 4.14 by @​lahma in Default Interop.ArrayConversion to LiveView for 4.14 sebastienros/jint#2728
• Cache array-like wrapper factories and materialize length lazily by @​lahma in Cache array-like wrapper factories and materialize length lazily sebastienros/jint#2730
• Convert primitive array-like wrapper elements without boxing by @​lahma in Convert primitive array-like wrapper elements without boxing sebastienros/jint#2731
• Add a compiled-invoker fast lane for single-candidate interop method calls by @​lahma in Add a compiled-invoker fast lane for single-candidate interop method calls sebastienros/jint#2733
• Intern JSON.parse string values and parse numbers off the span by @​lahma in Intern JSON.parse string values and parse numbers off the span sebastienros/jint#2732
• Default Interop.CacheRecentObjectWrappers to true for 4.14 by @​lahma in Default Interop.CacheRecentObjectWrappers to true for 4.14 sebastienros/jint#2734
• Harden LiveView array wrappers and interop wrapper caches for 4.14 by @​lahma in Harden LiveView array wrappers and interop wrapper caches for 4.14 sebastienros/jint#2735
• Keep execution-context depth balanced under raw constraint exceptions by @​lahma in Keep execution-context depth balanced under raw constraint exceptions sebastienros/jint#2736
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