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0.2.2 Feb 7, 2020
0.2.1 Jun 28, 2019
0.2.0 Mar 16, 2019
0.1.1 Nov 29, 2018
0.1.0 Nov 17, 2018

#673 in WebAssembly

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This crate provides the html! macro for building HTML documents inside your Rust code using roughly JSX compatible syntax.

Quick Preview

let mut doc: DOMTree<String> = html!(
            <title>"Hello Kitty"</title>
            <meta name=Metadata::Author content="Not Sanrio Co., Ltd"/>
            <h1>"Hello Kitty"</h1>
            <p class="official">
                "She is not a cat. She is a human girl."
            { (0..3).map(|_| html!(
                <p class="emphasis">
                    "Her name is Kitty White."
            )) }
            <p class="citation-needed">
                "We still don't know how she eats."
let doc_str = doc.to_string();


This macro largely follows JSX syntax, but with some differences:

  • Text nodes must be quoted, because there's only so much Rust's tokeniser can handle outside string literals. So, instead of <p>Hello</p>, you need to write <p>"Hello"</p>. (The parser will throw an error asking you to do this if you forget.)
  • Element attributes will accept simple Rust expressions, but the parser has its limits, as it's not a full Rust parser. You can use literals, variables, dotted properties, type constructors and single function or method calls. If you use something the parser isn't currently capable of handling, it will complain. You can put braces or parentheses around the expression if the parser doesn't understand it. You can use any Rust code inside a brace or parenthesis block.

Valid HTML5

The macro will only accept valid HTML5 tags, with no tags or attributes marked experimental or obsolete. If it won't accept something you want it to accept, we can discuss it over a pull request (experimental tags and attributes, in particular, are mostly omitted just for brevity, and you're welcome to implement them).

The structure validation is simplistic by necessity, as it defers to the type system: a few elements will have one or more required children, and any element which accepts children will have a restriction on the type of the children, usually a broad group as defined by the HTML spec. Many elements have restrictions on children of children, or require a particular ordering of optional elements, which isn't currently validated.

Attribute Values

Brace blocks in the attribute value position should return the expected type for the attribute. The type checker will complain if you return an unsupported type. You can also use literals or a few simple Rust expressions as attribute values (see the Syntax section above).

The html! macro will add an .into() call to the value expression, so that you can use any type that has an Into<A> trait defined for the actual attribute type A.

As a special case, if you use a string literal, the macro will instead use the FromStr<A> trait to try and parse the string literal into the expected type. This is extremely useful for eg. CSS classes, letting you type class="css-class-1 css-class-2" instead of going to the trouble of constructing a SpacedSet<Class>. The big caveat for this: currently, the macro is not able to validate the string at compile time, and the conversion will panic at runtime if the string is invalid.


let classList: SpacedSet<Class> = ["foo", "bar", "baz"].into();
        <div class="foo bar baz" />         // parses a string literal
        <div class=["foo", "bar", "baz"] /> // uses From<[&str, &str, &str]>
        <div class=classList />             // uses a variable in scope
        <div class={                        // evaluates a code block
            SpacedSet::from(["foo", "bar", "baz"])
        } />

Generated Nodes

Brace blocks in the child node position are expected to return an IntoIterator of DOMTrees. You can return single elements or text nodes, as they both implement IntoIterator for themselves. The macro will consume this iterator at runtime and insert the generated nodes as children in the expected position.


        { (1..=5).map(|i| html!(
            <li>{ text!("{}", i) }</li>
        )) }


You have two options for actually producing something useful from the DOM tree that comes out of the macro.

Render to a string

The DOM tree data structure implements Display, so you can call to_string() on it to render it to a String. If you plan to do this, the type of the tree should be DOMTree<String> to ensure you're not using any event handlers that can't be printed.

let doc: DOMTree<String> = html!(
    <p>"Hello Kitty"</p>
let doc_str = doc.to_string();
assert_eq!("<p>Hello Kitty</p>", doc_str);

Render to a virtual DOM

The DOM tree structure also implements a method called vnode(), which renders the tree to a tree of Nodes, which is a mirror of the generated tree with every attribute value rendered into Strings. You can walk this virtual DOM tree and use it to build an actual DOM tree with stdweb or pass it on to your favourite virtual DOM system.


Copyright 2018 Bodil Stokke

This software is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

Code of Conduct

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.


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