Context (cx) Methods

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The context (cx) is your handle to the JavaScript runtime. This is a cheat sheet of the methods you reach for most. (Method availability depends on the context type - FunctionContext, ModuleContext, etc. - and the enabled features.)

Construct JavaScript values

Call	Creates	Returns
cx.number(x)	number	Handle<JsNumber>
cx.string(s)	string	Handle<JsString>
cx.boolean(b)	boolean	Handle<JsBoolean>
cx.null()	null	Handle<JsNull>
cx.undefined()	undefined	Handle<JsUndefined>
cx.empty_object()	{}	Handle<JsObject>
cx.empty_array()	[]	Handle<JsArray>
cx.buffer(n)?	Node Buffer of n bytes	Handle<JsBuffer>
cx.array_buffer(n)?	ArrayBuffer of n bytes	Handle<JsArrayBuffer>
cx.boxed(value)	a JsBox wrapping Rust data	Handle<JsBox<T>>

Read arguments

Call	Does
cx.argument::<JsString>(0)?	read & type-check positional arg 0 (throws TypeError on mismatch)
cx.argument_opt(3)	read an argument that may be absent → Option<Handle<JsValue>>
cx.args()?	(with #[neon::export]) destructure all args into a Rust tuple
cx.args_opt::<(f64, f64)>()?	try to destructure args, returning Option for overloading

Access the runtime

Call	Does
cx.global("Array")?	get a global value by name
cx.global()	get the global object (then .get(&mut cx, "name")?)
cx.this()	the this value of the call
cx.lock()	acquire a lock for safe typed-array slice access

Exports (in #[neon::main])

Call	Does
cx.export_function("name", f)?	export a Rust function under a JS name
cx.export_value("name", v)?	export a constant or prebuilt value
neon::registered().export(&mut cx)?	export everything tagged with #[neon::export]

Async & threading

Call	Does
cx.task(|| ...)	run a closure on the worker pool, then .promise(...)
cx.promise()	create a (Deferred, Promise) pair to settle later
cx.channel()	get a Channel to schedule closures back on the main thread
handle.root(&mut cx)	persist a JS value as a Root across threads/async
root.into_inner(&mut cx)	turn a Root back into a Handle (on the main thread)

Throw errors

Call	Does
cx.throw_error("msg")	throw a JS Error; returns an Err result
result.or_throw(&mut cx)?	convert a Rust Result Err into a thrown JS exception

Reach for the prelude

use neon::prelude::*; brings the common traits and types (Context, Handle, the Js* types, JsResult, NeonResult) into scope so these methods resolve.