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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `JsCast` trait in crate `wasm_bindgen`."><meta name="keywords" content="rust, rustlang, rust-lang, JsCast"><title>wasm_bindgen::JsCast - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc trait"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../wasm_bindgen/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Trait JsCast</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.instanceof">instanceof</a><a href="#tymethod.unchecked_from_js">unchecked_from_js</a><a href="#tymethod.unchecked_from_js_ref">unchecked_from_js_ref</a></div><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.dyn_into">dyn_into</a><a href="#method.dyn_ref">dyn_ref</a><a href="#method.has_type">has_type</a><a href="#method.is_instance_of">is_instance_of</a><a href="#method.is_type_of">is_type_of</a><a href="#method.unchecked_into">unchecked_into</a><a href="#method.unchecked_ref">unchecked_ref</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='index.html'>wasm_bindgen</a></p><script>window.sidebarCurrent = {name: 'JsCast', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/wasm_bindgen/cast.rs.html#15-156' title='goto source code'>[src]</a></span><span class='in-band'>Trait <a href='index.html'>wasm_bindgen</a>::<wbr><a class="trait" href=''>JsCast</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub trait JsCast <span class="where fmt-newline">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.AsRef.html" title="trait core::convert::AsRef">AsRef</a><<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/convert/trait.Into.html" title="trait core::convert::Into">Into</a><<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>>, </span>{
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fn <a href='#tymethod.instanceof' class='fnname'>instanceof</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a>;
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<div class='item-spacer'></div> fn <a href='#tymethod.unchecked_from_js' class='fnname'>unchecked_from_js</a>(val: <a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> Self;
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<div class='item-spacer'></div> fn <a href='#tymethod.unchecked_from_js_ref' class='fnname'>unchecked_from_js_ref</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>Self;
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fn <a href='#method.has_type' class='fnname'>has_type</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a><br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.dyn_into' class='fnname'>dyn_into</a><T>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><T, Self><br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.dyn_ref' class='fnname'>dyn_ref</a><T>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T><br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.unchecked_into' class='fnname'>unchecked_into</a><T>(self) -> T<br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.unchecked_ref' class='fnname'>unchecked_ref</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T<br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.is_instance_of' class='fnname'>is_instance_of</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a><br> <span class="where">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.is_type_of' class='fnname'>is_type_of</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a> { ... }
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}</pre></div><div class='docblock'><p>A trait for checked and unchecked casting between JS types.</p>
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<p>Specified <a href="https://github.com/rustwasm/rfcs/pull/2">in an RFC</a> this trait is intended to provide support for
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casting JS values between differnet types of one another. In JS there aren't
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many static types but we've ascribed JS values with static types in Rust,
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yet they often need to be switched to other types temporarily! This trait
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provides both checked and unchecked casting into various kinds of values.</p>
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<p>This trait is automatically implemented for any type imported in a
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<code>#[wasm_bindgen]</code> <code>extern</code> block.</p>
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</div>
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<h2 id='required-methods' class='small-section-header'>Required methods<a href='#required-methods' class='anchor'></a></h2><div class='methods'><h3 id='tymethod.instanceof' class='method'><code id='instanceof.v'>fn <a href='#tymethod.instanceof' class='fnname'>instanceof</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a></code></h3><div class='docblock'><p>Performs a dynamic <code>instanceof</code> check to see whether the <code>JsValue</code>
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provided is an instance of this type.</p>
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<p>This is intended to be an internal implementation detail, you likely
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won't need to call this. It's generally called through the
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<code>is_instance_of</code> method instead.</p>
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</div><h3 id='tymethod.unchecked_from_js' class='method'><code id='unchecked_from_js.v'>fn <a href='#tymethod.unchecked_from_js' class='fnname'>unchecked_from_js</a>(val: <a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> Self</code></h3><div class='docblock'><p>Performs a zero-cost unchecked conversion from a <code>JsValue</code> into an
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instance of <code>Self</code></p>
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<p>This is intended to be an internal implementation detail, you likely
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won't need to call this.</p>
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</div><h3 id='tymethod.unchecked_from_js_ref' class='method'><code id='unchecked_from_js_ref.v'>fn <a href='#tymethod.unchecked_from_js_ref' class='fnname'>unchecked_from_js_ref</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>Self</code></h3><div class='docblock'><p>Performs a zero-cost unchecked conversion from a <code>&JsValue</code> into an
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instance of <code>&Self</code>.</p>
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<p>Note the safety of this method, which basically means that <code>Self</code> must
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be a newtype wrapper around <code>JsValue</code>.</p>
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<p>This is intended to be an internal implementation detail, you likely
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won't need to call this.</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<h2 id='provided-methods' class='small-section-header'>Provided methods<a href='#provided-methods' class='anchor'></a></h2><div class='methods'><h3 id='method.has_type' class='method'><code id='has_type.v'>fn <a href='#method.has_type' class='fnname'>has_type</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a> <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Test whether this JS value has a type <code>T</code>.</p>
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<p>This method will dynamically check to see if this JS object can be
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casted to the JS object of type <code>T</code>. Usually this uses the <code>instanceof</code>
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operator. This also works with primitive types like
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booleans/strings/numbers as well as cross-realm object like <code>Array</code>
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which can originate from other iframes.</p>
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<p>In general this is intended to be a more robust version of
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<code>is_instance_of</code>, but if you want strictly the <code>instanceof</code> operator
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it's recommended to use that instead.</p>
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</div><h3 id='method.dyn_into' class='method'><code id='dyn_into.v'>fn <a href='#method.dyn_into' class='fnname'>dyn_into</a><T>(self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><T, Self> <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Performs a dynamic cast (checked at runtime) of this value into the
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target type <code>T</code>.</p>
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<p>This method will return <code>Err(self)</code> if <code>self.has_type::<T>()</code>
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returns <code>false</code>, and otherwise it will return <code>Ok(T)</code> manufactured with
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an unchecked cast (verified correct via the <code>has_type</code> operation).</p>
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</div><h3 id='method.dyn_ref' class='method'><code id='dyn_ref.v'>fn <a href='#method.dyn_ref' class='fnname'>dyn_ref</a><T>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T> <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Performs a dynamic cast (checked at runtime) of this value into the
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target type <code>T</code>.</p>
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<p>This method will return <code>None</code> if <code>self.has_type::<T>()</code>
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returns <code>false</code>, and otherwise it will return <code>Some(&T)</code> manufactured
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with an unchecked cast (verified correct via the <code>has_type</code> operation).</p>
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</div><h3 id='method.unchecked_into' class='method'><code id='unchecked_into.v'>fn <a href='#method.unchecked_into' class='fnname'>unchecked_into</a><T>(self) -> T <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Performs a zero-cost unchecked cast into the specified type.</p>
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<p>This method will convert the <code>self</code> value to the type <code>T</code>, where both
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<code>self</code> and <code>T</code> are simple wrappers around <code>JsValue</code>. This method <strong>does
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not check whether <code>self</code> is an instance of <code>T</code></strong>. If used incorrectly
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then this method may cause runtime exceptions in both Rust and JS, this
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should be used with caution.</p>
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</div><h3 id='method.unchecked_ref' class='method'><code id='unchecked_ref.v'>fn <a href='#method.unchecked_ref' class='fnname'>unchecked_ref</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Performs a zero-cost unchecked cast into a reference to the specified
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type.</p>
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<p>This method will convert the <code>self</code> value to the type <code>T</code>, where both
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<code>self</code> and <code>T</code> are simple wrappers around <code>JsValue</code>. This method <strong>does
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not check whether <code>self</code> is an instance of <code>T</code></strong>. If used incorrectly
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then this method may cause runtime exceptions in both Rust and JS, this
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should be used with caution.</p>
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<p>This method, unlike <code>unchecked_into</code>, does not consume ownership of
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<code>self</code> and instead works over a shared reference.</p>
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</div><h3 id='method.is_instance_of' class='method'><code id='is_instance_of.v'>fn <a href='#method.is_instance_of' class='fnname'>is_instance_of</a><T>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a> <span class="where fmt-newline">where<br> T: <a class="trait" href="../wasm_bindgen/trait.JsCast.html" title="trait wasm_bindgen::JsCast">JsCast</a>, </span></code></h3><div class='docblock'><p>Test whether this JS value is an instance of the type <code>T</code>.</p>
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<p>This method performs a dynamic check (at runtime) using the JS
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<code>instanceof</code> operator. This method returns <code>self instanceof T</code>.</p>
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<p>Note that <code>instanceof</code> does not always work with primitive values or
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across different realms (e.g. iframes). If you're not sure whether you
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specifically need only <code>instanceof</code> it's recommended to use <code>has_type</code>
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instead.</p>
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</div><h3 id='method.is_type_of' class='method'><code id='is_type_of.v'>fn <a href='#method.is_type_of' class='fnname'>is_type_of</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a></code></h3><div class='docblock'><p>Performs a dynamic check to see whether the <code>JsValue</code> provided
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is a value of this type.</p>
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<p>Unlike <code>instanceof</code>, this can be specialised to use a custom check by
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adding a <code>#[wasm_bindgen(is_type_of = callback)]</code> attribute to the
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type import declaration.</p>
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<p>Other than that, this is intended to be an internal implementation
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detail of <code>has_type</code> and you likely won't need to call this.</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<h2 id='implementors' class='small-section-header'>Implementors<a href='#implementors' class='anchor'></a></h2><div class='item-list' id='implementors-list'><h3 id='impl-JsCast' class='impl'><code class='in-band'>impl JsCast for <a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a></code><a href='#impl-JsCast' class='anchor'></a><a class='srclink' href='../src/wasm_bindgen/lib.rs.html#444-458' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='method.instanceof' class="method hidden"><code id='instanceof.v-1'>fn <a href='#method.instanceof' class='fnname'>instanceof</a>(_val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a></code><a class='srclink' href='../src/wasm_bindgen/lib.rs.html#447-449' title='goto source code'>[src]</a></h4><h4 id='method.unchecked_from_js' class="method hidden"><code id='unchecked_from_js.v-1'>fn <a href='#method.unchecked_from_js' class='fnname'>unchecked_from_js</a>(val: <a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> Self</code><a class='srclink' href='../src/wasm_bindgen/lib.rs.html#451-453' title='goto source code'>[src]</a></h4><h4 id='method.unchecked_from_js_ref' class="method hidden"><code id='unchecked_from_js_ref.v-1'>fn <a href='#method.unchecked_from_js_ref' class='fnname'>unchecked_from_js_ref</a>(val: &<a class="struct" href="../wasm_bindgen/struct.JsValue.html" title="struct wasm_bindgen::JsValue">JsValue</a>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>Self</code><a class='srclink' href='../src/wasm_bindgen/lib.rs.html#455-457' title='goto source code'>[src]</a></h4></div></div><span class='loading-content'>Loading content...</span><script type="text/javascript" src="../implementors/wasm_bindgen/trait.JsCast.js" async></script></section><section id="search" class="content hidden"></section><section class="footer"></section><script>window.rootPath = "../";window.currentCrate = "wasm_bindgen";</script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html> |