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<ol class="chapter"><li class="affix"><a href="../../introduction.html">Introduction</a></li><li class="spacer"></li><li><a href="../../examples/index.html"><strong aria-hidden="true">1.</strong> Examples</a></li><li><ol class="section"><li><a href="../../examples/hello-world.html"><strong aria-hidden="true">1.1.</strong> Hello, World!</a></li><li><a href="../../examples/console-log.html"><strong aria-hidden="true">1.2.</strong> Using console.log</a></li><li><a href="../../examples/add.html"><strong aria-hidden="true">1.3.</strong> Small wasm files</a></li><li><a href="../../examples/without-a-bundler.html"><strong aria-hidden="true">1.4.</strong> Without a Bundler</a></li><li><a href="../../examples/wasm2js.html"><strong aria-hidden="true">1.5.</strong> Converting WebAssembly to JS</a></li><li><a href="../../examples/import-js.html"><strong aria-hidden="true">1.6.</strong> Importing functions from JS</a></li><li><a href="../../examples/char.html"><strong aria-hidden="true">1.7.</strong> Working with char</a></li><li><a href="../../examples/wasm-in-wasm.html"><strong aria-hidden="true">1.8.</strong> js-sys: WebAssembly in WebAssembly</a></li><li><a href="../../examples/dom.html"><strong aria-hidden="true">1.9.</strong> web-sys: DOM hello world</a></li><li><a href="../../examples/closures.html"><strong aria-hidden="true">1.10.</strong> web-sys: Closures</a></li><li><a href="../../examples/performance.html"><strong aria-hidden="true">1.11.</strong> web-sys: performance.now</a></li><li><a href="../../examples/fetch.html"><strong aria-hidden="true">1.12.</strong> web-sys: using fetch</a></li><li><a href="../../examples/2d-canvas.html"><strong aria-hidden="true">1.13.</strong> web-sys: canvas hello world</a></li><li><a href="../../examples/julia.html"><strong aria-hidden="true">1.14.</strong> web-sys: canvas Julia set</a></li><li><a href="../../examples/web-audio.html"><strong aria-hidden="true">1.15.</strong> web-sys: WebAudio</a></li><li><a href="../../examples/webgl.html"><strong aria-hidden="true">1.16.</strong> web-sys: WebGL</a></li><li><a href="../../examples/websockets.html"><strong aria-hidden="true">1.17.</strong> web-sys: WebSockets</a></li><li><a href="../../examples/webrtc_datachannel.html"><strong aria-hidden="true">1.18.</strong> web-sys: WebRTC DataChannel</a></li><li><a href="../../examples/request-animation-frame.html"><strong aria-hidden="true">1.19.</strong> web-sys: requestAnimationFrame</a></li><li><a href="../../examples/paint.html"><strong aria-hidden="true">1.20.</strong> web-sys: A Simple Paint Program</a></li><li><a href="../../examples/raytrace.html"><strong aria-hidden="true">1.21.</strong> Parallel Raytracing</a></li><li><a href="../../examples/todomvc.html"><strong aria-hidden="true">1.22.</strong> web-sys: A TODO MVC App</a></li></ol></li><li><a href="../../reference/index.html"><strong aria-hidden="true">2.</strong> Reference</a></li><li><ol class="section"><li><a href="../../reference/deployment.html"><strong aria-hidden="true">2.1.</strong> Deployment</a></li><li><a href="../../reference/js-snippets.html"><strong aria-hidden="true">2.2.</strong> JS snippets</a></li><li><a href="../../reference/passing-rust-closures-to-js.html"><strong aria-hidden="true">2.3.</strong> Passing Rust Closures to JS</a></li><li><a href="../../reference/receiving-js-closures-in-rust.html"><strong aria-hidden="true">2.4.</strong> Receiving JS Closures in Rust</a></li><li><a href="../../reference/js-promises-and-rust-futures.html"><strong aria-hidden="true">2.5.</strong> Promises and Futures</a></li><li><a href="../../reference/iterating-over-js-values.html"><strong aria-hidden="true">2.6.</strong> Iterating over JS Values</a></li><li><a href="../../reference/arbitrary-data-with-serde.html"><strong aria-hidden="true">2.7.</strong> Arbitrary Data with Serde</a></li><li><a href="../../reference/accessing-properties-of-untyped-js-values.html"><strong aria-hidden="true">2.8.</strong> Accessing Properties of Untyped JS Values</a></li><li><a href="../../reference/working-with-duck-typed-interfaces.html"><strong aria-hidden="true">2.9.</strong> Working with Duck-Typed Interfaces</a></li><li><a href="../../reference/cli.html"><strong aria-hidden="true">2.10.</strong> Command Line Interface</a></li><li><a href="../../reference/optimize-size.html"><strong aria-hidden="true">2.11.</strong> Optimizing for Size</a></li><li><a href="../../reference/rust-targets.html"><strong aria-hidden="true">2.12.</strong> Supported Rust Targets</a></li><li><a href="../../reference/browser-support.html"><strong aria-hidden="true">2.13.</strong> Supported Browsers</a></li><li><a href="../../reference/types.html"><strong aria-hidden="true">2.14.</strong> Supported Types</a></li><li><ol class="section"><li><a href="../../reference/types/imported-js-types.html"><strong aria-hidden="true">2.14.1.</strong> Imported JavaScript Types</a></li><li><a href="../../reference/types/exported-rust-types.html"><strong aria-hidden="true">2.14.2.</strong> Exported Rust Types</a></li><li><a href="../../reference/types/jsvalue.html"><strong aria-hidden="true">2.14.3.</strong> JsValue</a></li><li><a href="../../reference/types/boxed-jsvalue-slice.html"><strong aria-hidden="true">2.14.4.</strong> Box<[JsValue]></a></li><li><a href="../../reference/types/pointers.html"><strong aria-hidden="true">2.14.5.</strong> *const T and *mut T</a></li><li><a href="../../reference/types/numbers.html"><strong aria-hidden="true">2.14.6.</strong> Numbers</a></li><li><a href="../../reference/types/bool.html"><strong aria-hidden="true">2.14.7.</strong> bool</a></li><li><a href="../../reference/types/char.html"><strong aria-hidden="true">2.14.8.</strong> char</a></li><li><a href="../../reference/types/str.html"><strong aria-hidden="true">2.14.9.</strong> str</a></li><li><a href="../../reference/types/string.html"><strong aria-hidden="true">2.14.10.</strong> String</a></li><li><a href="../../reference/types/number-slices.html"><strong aria-hidden="true">2.14.11.</strong> Number Slices</a></li><li><a href="../../reference/types/boxed-number-slices.html"><strong aria-hidden="true">2.14.12.</strong> Boxed Number Slices</a></li><li><a href="../../reference/types/result.html"><strong aria-hidden="true">2.14.13.</strong> Result<T, JsValue></a></li></ol></li><li><a href="../../reference/attributes/index.html"><strong aria-hidden="true">2.15.</strong> #[wasm_bindgen] Attributes</a></li><li><ol class="section"><li><a href="../../reference/attributes/on-js-imports/index.html"><strong aria-hidden="true">2.15.1.</strong> On JavaScript Imports</a></li><li><ol class="section"><li><a href="../../reference/attributes/on-js-imports/catch.html"><strong aria-hidden="true">2.15.1.1.</strong> catch</a></li><li><a href="../../reference/attributes/on-js-imports/constructor.html"><strong aria-hidden="true">2.15.1.2.</strong> constructor</a></li><li><a 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js_namespace</a></li><li><a href="../../reference/attributes/on-js-imports/method.html"><strong aria-hidden="true">2.15.1.10.</strong> method</a></li><li><a href="../../reference/attributes/on-js-imports/module.html"><strong aria-hidden="true">2.15.1.11.</strong> module = "blah"</a></li><li><a href="../../reference/attributes/on-js-imports/raw_module.html"><strong aria-hidden="true">2.15.1.12.</strong> raw_module = "blah"</a></li><li><a href="../../reference/attributes/on-js-imports/static_method_of.html"><strong aria-hidden="true">2.15.1.13.</strong> static_method_of = Blah</a></li><li><a href="../../reference/attributes/on-js-imports/structural.html"><strong aria-hidden="true">2.15.1.14.</strong> structural</a></li><li><a href="../../reference/attributes/on-js-imports/variadic.html"><strong aria-hidden="true">2.15.1.15.</strong> variadic</a></li><li><a href="../../reference/attributes/on-js-imports/vendor_prefix.html"><strong aria-hidden="true">2.15.1.16.</strong> vendor_prefix</a></li></ol></li><li><a href="../../reference/attributes/on-rust-exports/index.html"><strong aria-hidden="true">2.15.2.</strong> On Rust Exports</a></li><li><ol class="section"><li><a href="../../reference/attributes/on-rust-exports/constructor.html"><strong aria-hidden="true">2.15.2.1.</strong> constructor</a></li><li><a href="../../reference/attributes/on-rust-exports/js_name.html"><strong aria-hidden="true">2.15.2.2.</strong> js_name = Blah</a></li><li><a href="../../reference/attributes/on-rust-exports/readonly.html"><strong aria-hidden="true">2.15.2.3.</strong> readonly</a></li><li><a href="../../reference/attributes/on-rust-exports/skip.html"><strong aria-hidden="true">2.15.2.4.</strong> skip</a></li><li><a href="../../reference/attributes/on-rust-exports/start.html"><strong aria-hidden="true">2.15.2.5.</strong> start</a></li><li><a href="../../reference/attributes/on-rust-exports/typescript_custom_section.html"><strong aria-hidden="true">2.15.2.6.</strong> typescript_custom_section</a></li><li><a href="../../reference/attributes/on-rust-exports/getter-and-setter.html"><strong aria-hidden="true">2.15.2.7.</strong> getter and setter</a></li><li><a href="../../reference/attributes/on-rust-exports/inspectable.html"><strong aria-hidden="true">2.15.2.8.</strong> inspectable</a></li><li><a href="../../reference/attributes/on-rust-exports/skip_typescript.html"><strong aria-hidden="true">2.15.2.9.</strong> skip_typescript</a></li><li><a href="../../reference/attributes/on-rust-exports/typescript_type.html"><strong aria-hidden="true">2.15.2.10.</strong> typescript_type</a></li></ol></li></ol></li></ol></li><li><a href="../../web-sys/index.html"><strong aria-hidden="true">3.</strong> web-sys</a></li><li><ol class="section"><li><a href="../../web-sys/using-web-sys.html"><strong aria-hidden="true">3.1.</strong> Using web-sys</a></li><li><a href="../../web-sys/cargo-features.html"><strong aria-hidden="true">3.2.</strong> Cargo Features</a></li><li><a href="../../web-sys/function-overloads.html"><strong aria-hidden="true">3.3.</strong> Function Overloads</a></li><li><a href="../../web-sys/type-translations.html"><strong aria-hidden="true">3.4.</strong> Type Translations</a></li><li><a href="../../web-sys/inheritance.html"><strong aria-hidden="true">3.5.</strong> Inheritance</a></li><li><a href="../../web-sys/unstable-apis.html"><strong aria-hidden="true">3.6.</strong> Unstable APIs</a></li></ol></li><li><a href="../../wasm-bindgen-test/index.html"><strong aria-hidden="true">4.</strong> Testing with wasm-bindgen-test</a></li><li><ol class="section"><li><a href="../../wasm-bindgen-test/usage.html"><strong aria-hidden="true">4.1.</strong> Usage</a></li><li><a href="../../wasm-bindgen-test/asynchronous-tests.html"><strong aria-hidden="true">4.2.</strong> Writing Asynchronous Tests</a></li><li><a href="../../wasm-bindgen-test/browsers.html"><strong aria-hidden="true">4.3.</strong> Testing in Headless Browsers</a></li><li><a href="../../wasm-bindgen-test/continuous-integration.html"><strong aria-hidden="true">4.4.</strong> Continuous Integration</a></li></ol></li><li><a href="../../contributing/index.html"><strong aria-hidden="true">5.</strong> Contributing to wasm-bindgen</a></li><li><ol class="section"><li><a href="../../contributing/testing.html"><strong aria-hidden="true">5.1.</strong> Testing</a></li><li><a href="../../contributing/design/index.html"><strong aria-hidden="true">5.2.</strong> Internal Design</a></li><li><ol class="section"><li><a href="../../contributing/design/js-objects-in-rust.html"><strong aria-hidden="true">5.2.1.</strong> JS Objects in Rust</a></li><li><a href="../../contributing/design/exporting-rust.html"><strong aria-hidden="true">5.2.2.</strong> Exporting a function to JS</a></li><li><a href="../../contributing/design/exporting-rust-struct.html"><strong aria-hidden="true">5.2.3.</strong> Exporting a struct to JS</a></li><li><a href="../../contributing/design/importing-js.html"><strong aria-hidden="true">5.2.4.</strong> Importing a function from JS</a></li><li><a href="../../contributing/design/importing-js-struct.html" class="active"><strong aria-hidden="true">5.2.5.</strong> Importing a class from JS</a></li><li><a href="../../contributing/design/rust-type-conversions.html"><strong aria-hidden="true">5.2.6.</strong> Rust Type conversions</a></li><li><a href="../../contributing/design/describe.html"><strong aria-hidden="true">5.2.7.</strong> Types in wasm-bindgen</a></li></ol></li><li><a href="../../contributing/js-sys/index.html"><strong aria-hidden="true">5.3.</strong> js-sys</a></li><li><ol class="section"><li><a href="../../contributing/js-sys/testing.html"><strong aria-hidden="true">5.3.1.</strong> Testing</a></li><li><a href="../../contributing/js-sys/adding-more-apis.html"><strong aria-hidden="true">5.3.2.</strong> Adding More APIs</a></li></ol></li><li><a href="../../contributing/web-sys/index.html"><strong aria-hidden="true">5.4.</strong> web-sys</a></li><li><ol class="section"><li><a href="../../contributing/web-sys/overview.html"><strong aria-hidden="true">5.4.1.</strong> Overview</a></li><li><a href="../../contributing/web-sys/testing.html"><strong aria-hidden="true">5.4.2.</strong> Testing</a></li><li><a href="../../contributing/web-sys/logging.html"><strong aria-hidden="true">5.4.3.</strong> Logging</a></li><li><a href="../../contributing/web-sys/supporting-more-web-apis.html"><strong aria-hidden="true">5.4.4.</strong> Supporting More Web APIs</a></li></ol></li><li><a href="../../contributing/publishing.html"><strong aria-hidden="true">5.5.</strong> Publishing</a></li><li><a href="../../contributing/team.html"><strong aria-hidden="true">5.6.</strong> Team</a></li></ol></li></ol>
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<div id="content" class="content">
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<main>
|
|
<h1><a class="header" href="#importing-a-class-from-js" id="importing-a-class-from-js">Importing a class from JS</a></h1>
|
|
<p>Just like with functions after we've started exporting we'll also want to
|
|
import! Now that we've exported a <code>class</code> to JS we'll want to also be able to
|
|
import classes in Rust as well to invoke methods and such. Since JS classes are
|
|
in general just JS objects the bindings here will look pretty similar to the JS
|
|
object bindings describe above.</p>
|
|
<p>As usual though, let's dive into an example!</p>
|
|
<pre><pre class="playpen"><code class="language-rust">
|
|
# #![allow(unused_variables)]
|
|
#fn main() {
|
|
#[wasm_bindgen(module = "./bar")]
|
|
extern "C" {
|
|
type Bar;
|
|
|
|
#[wasm_bindgen(constructor)]
|
|
fn new(arg: i32) -> Bar;
|
|
|
|
#[wasm_bindgen(js_namespace = Bar)]
|
|
fn another_function() -> i32;
|
|
|
|
#[wasm_bindgen(method)]
|
|
fn get(this: &Bar) -> i32;
|
|
|
|
#[wasm_bindgen(method)]
|
|
fn set(this: &Bar, val: i32);
|
|
|
|
#[wasm_bindgen(method, getter)]
|
|
fn property(this: &Bar) -> i32;
|
|
|
|
#[wasm_bindgen(method, setter)]
|
|
fn set_property(this: &Bar, val: i32);
|
|
}
|
|
|
|
fn run() {
|
|
let bar = Bar::new(Bar::another_function());
|
|
let x = bar.get();
|
|
bar.set(x + 3);
|
|
|
|
bar.set_property(bar.property() + 6);
|
|
}
|
|
#}</code></pre></pre>
|
|
<p>Unlike our previous imports, this one's a bit more chatty! Remember that one of
|
|
the goals of <code>wasm-bindgen</code> is to use native Rust syntax wherever possible, so
|
|
this is mostly intended to use the <code>#[wasm_bindgen]</code> attribute to interpret
|
|
what's written down in Rust. Now there's a few attribute annotations here, so
|
|
let's go through one-by-one:</p>
|
|
<ul>
|
|
<li><code>#[wasm_bindgen(module = "./bar")]</code> - seen before with imports this is declare
|
|
where all the subsequent functionality is imported from. For example the <code>Bar</code>
|
|
type is going to be imported from the <code>./bar</code> module.</li>
|
|
<li><code>type Bar</code> - this is a declaration of JS class as a new type in Rust. This
|
|
means that a new type <code>Bar</code> is generated which is "opaque" but is represented
|
|
as internally containing a <code>JsValue</code>. We'll see more on this later.</li>
|
|
<li><code>#[wasm_bindgen(constructor)]</code> - this indicates that the binding's name isn't
|
|
actually used in JS but rather translates to <code>new Bar()</code>. The return value of
|
|
this function must be a bare type, like <code>Bar</code>.</li>
|
|
<li><code>#[wasm_bindgen(js_namespace = Bar)]</code> - this attribute indicates that the
|
|
function declaration is namespaced through the <code>Bar</code> class in JS.</li>
|
|
<li><code>#[wasm_bindgen(static_method_of = SomeJsClass)]</code> - this attribute is similar
|
|
to <code>js_namespace</code>, but instead of producing a free function, produces a static
|
|
method of <code>SomeJsClass</code>.</li>
|
|
<li><code>#[wasm_bindgen(method)]</code> - and finally, this attribute indicates that a
|
|
method call is going to happen. The first argument must be a JS struct, like
|
|
<code>Bar</code>, and the call in JS looks like <code>Bar.prototype.set.call(...)</code>.</li>
|
|
</ul>
|
|
<p>With all that in mind, let's take a look at the JS generated.</p>
|
|
<pre><code class="language-js">import * as wasm from './foo_bg';
|
|
|
|
import { Bar } from './bar';
|
|
|
|
// other support functions omitted...
|
|
|
|
export function __wbg_s_Bar_new() {
|
|
return addHeapObject(new Bar());
|
|
}
|
|
|
|
const another_function_shim = Bar.another_function;
|
|
export function __wbg_s_Bar_another_function() {
|
|
return another_function_shim();
|
|
}
|
|
|
|
const get_shim = Bar.prototype.get;
|
|
export function __wbg_s_Bar_get(ptr) {
|
|
return shim.call(getObject(ptr));
|
|
}
|
|
|
|
const set_shim = Bar.prototype.set;
|
|
export function __wbg_s_Bar_set(ptr, arg0) {
|
|
set_shim.call(getObject(ptr), arg0)
|
|
}
|
|
|
|
const property_shim = Object.getOwnPropertyDescriptor(Bar.prototype, 'property').get;
|
|
export function __wbg_s_Bar_property(ptr) {
|
|
return property_shim.call(getObject(ptr));
|
|
}
|
|
|
|
const set_property_shim = Object.getOwnPropertyDescriptor(Bar.prototype, 'property').set;
|
|
export function __wbg_s_Bar_set_property(ptr, arg0) {
|
|
set_property_shim.call(getObject(ptr), arg0)
|
|
}
|
|
</code></pre>
|
|
<p>Like when importing functions from JS we can see a bunch of shims are generated
|
|
for all the relevant functions. The <code>new</code> static function has the
|
|
<code>#[wasm_bindgen(constructor)]</code> attribute which means that instead of any
|
|
particular method it should actually invoke the <code>new</code> constructor instead (as
|
|
we see here). The static function <code>another_function</code>, however, is dispatched as
|
|
<code>Bar.another_function</code>.</p>
|
|
<p>The <code>get</code> and <code>set</code> functions are methods so they go through <code>Bar.prototype</code>,
|
|
and otherwise their first argument is implicitly the JS object itself which is
|
|
loaded through <code>getObject</code> like we saw earlier.</p>
|
|
<p>Some real meat starts to show up though on the Rust side of things, so let's
|
|
take a look:</p>
|
|
<pre><pre class="playpen"><code class="language-rust">
|
|
# #![allow(unused_variables)]
|
|
#fn main() {
|
|
pub struct Bar {
|
|
obj: JsValue,
|
|
}
|
|
|
|
impl Bar {
|
|
fn new() -> Bar {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_new() -> u32;
|
|
}
|
|
unsafe {
|
|
let ret = __wbg_s_Bar_new();
|
|
Bar { obj: JsValue::__from_idx(ret) }
|
|
}
|
|
}
|
|
|
|
fn another_function() -> i32 {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_another_function() -> i32;
|
|
}
|
|
unsafe {
|
|
__wbg_s_Bar_another_function()
|
|
}
|
|
}
|
|
|
|
fn get(&self) -> i32 {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_get(ptr: u32) -> i32;
|
|
}
|
|
unsafe {
|
|
let ptr = self.obj.__get_idx();
|
|
let ret = __wbg_s_Bar_get(ptr);
|
|
return ret
|
|
}
|
|
}
|
|
|
|
fn set(&self, val: i32) {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_set(ptr: u32, val: i32);
|
|
}
|
|
unsafe {
|
|
let ptr = self.obj.__get_idx();
|
|
__wbg_s_Bar_set(ptr, val);
|
|
}
|
|
}
|
|
|
|
fn property(&self) -> i32 {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_property(ptr: u32) -> i32;
|
|
}
|
|
unsafe {
|
|
let ptr = self.obj.__get_idx();
|
|
let ret = __wbg_s_Bar_property(ptr);
|
|
return ret
|
|
}
|
|
}
|
|
|
|
fn set_property(&self, val: i32) {
|
|
extern "C" {
|
|
fn __wbg_s_Bar_set_property(ptr: u32, val: i32);
|
|
}
|
|
unsafe {
|
|
let ptr = self.obj.__get_idx();
|
|
__wbg_s_Bar_set_property(ptr, val);
|
|
}
|
|
}
|
|
}
|
|
|
|
impl WasmBoundary for Bar {
|
|
// ...
|
|
}
|
|
|
|
impl ToRefWasmBoundary for Bar {
|
|
// ...
|
|
}
|
|
#}</code></pre></pre>
|
|
<p>In Rust we're seeing that a new type, <code>Bar</code>, is generated for this import of a
|
|
class. The type <code>Bar</code> internally contains a <code>JsValue</code> as an instance of <code>Bar</code>
|
|
is meant to represent a JS object stored in our module's stack/slab. This then
|
|
works mostly the same way that we saw JS objects work in the beginning.</p>
|
|
<p>When calling <code>Bar::new</code> we'll get an index back which is wrapped up in <code>Bar</code>
|
|
(which is itself just a <code>u32</code> in memory when stripped down). Each function then
|
|
passes the index as the first argument and otherwise forwards everything along
|
|
in Rust.</p>
|
|
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