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On this page 8

ArrayBuffer

Beyond the classic surface, zig-js implements the modern buffer proposals:

MemberBehaviour
resizable, maxByteLength, resize()Resizable buffers, with length-tracking views following the buffer.
transfer(), transferToFixedLength()Ownership transfer; the source detaches.
transferToImmutable(), sliceToImmutable(), immutableImmutable buffers.
detachedReflects detach state from transfer or structured clone.
slice()Standard copy.

Detached-buffer checks are enforced at every access site, and a resize is synchronized against bulk copies (Atomics operations, copyWithin, slice) so a concurrent resize cannot tear a copy — see Memory model for exactly which races are engine races and which are program races.

Typed arrays

All twelve element types share one %TypedArray%.prototype:

Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, Float16Array, Float32Array, Float64Array, BigInt64Array, BigUint64Array.

BigInt64Array and BigUint64Array read and write BigInt values; the rest use Numbers. %TypedArray% itself is the abstract superclass constructor — it can neither be called nor constructed directly.

Length-tracking views over resizable buffers, out-of-bounds handling after a resize, and the immutable-buffer write rejection are all implemented.

DataView

Byte-precise access with explicit endianness across every element width, including getFloat16 / setFloat16 and the BigInt accessors, with the same detach and bounds checks.

SharedArrayBuffer

Installed when the context allows it. Storage is refcounted (src/shared_buffer.zig), so the same backing memory can be retained across agents, Workers, and shared-realm Threads while each holds its own JavaScript object.

A conformance-shaped knob exists for engine-shell parity: a context can leave property-mode Atomics installed while hiding the global SharedArrayBuffer constructor, modelling --useSharedArrayBuffer=0.

Atomics

Two modes are supported:

  • Typed-array Atomics — add, and, compareExchange, exchange, load, or, store, sub, xor, isLockFree, plus wait, waitAsync, and notify against the shared waiter table in src/agent.zig.
  • Property-mode Atomics — the same operations against ordinary object properties, used by the shared-realm Thread model.

With enable_threads, Atomics additionally carries the proposal-aligned Atomics.Mutex and Atomics.Condition, alongside the standalone Lock, Condition, and ThreadLocal globals. See Concurrency.

Blocking and [[CanBlock]]

Whether a blocking Atomics.wait is permitted is a host decision. Conformance and embedder harnesses model [[CanBlock]]; when it is false, blocking APIs throw if they would have to park, while non-blocking fast paths and the async forms (waitAsync) continue to work.

Structured clone and transfer

src/structured_clone.zig implements the wire format used by structuredClone() and by Worker postMessage, including ArrayBuffer transfer with detach and SharedArrayBuffer retention (shared, not copied).

WebAssembly memory

Wasm linear memory, including shared memory with atomic access and wait32/wait64/notify, is documented in WebAssembly.