Conditional rendering

If blocks

To conditionally render some markup, we wrap it in an if block:

if

use yew::prelude::*;

html! {
    if true {
        <p>{ "True case" }</p>
    }
};

if - else

use yew::prelude::*;
let some_condition = true;

html! {
    if some_condition {
        <p>{ "True case" }</p>
    } else {
        <p>{ "False case" }</p>
    }
};

if let

use yew::prelude::*;
let some_text = Some("text");

html! {
    if let Some(text) = some_text {
        <p>{ text }</p>
    }
};

if let else

use yew::prelude::*;
let some_text = Some("text");

html! {
    if let Some(text) = some_text {
        <p>{ text }</p>
    } else {
        <p>{ "False case" }</p>
    }
};

Let bindings

Braced bodies support let bindings before html children, as well as multiple children directly:

use yew::prelude::*;

html! {
    if condition {
        let label = format!("count: {count}");
        <h2>{"Result"}</h2>
        <span>{label}</span>
    } else {
        "nothing"
    }
};

let bindings must appear before any html children and cannot be interleaved with them.

Match blocks

match expressions work directly in html!, following the same pattern as if/else:

match

use yew::prelude::*;

let value: Option<String> = Some("hello".into());

html! {
    match value {
        Some(text) => <p>{text}</p>,
        None => <p>{"Nothing here"}</p>,
    }
};

If guards

use yew::prelude::*;

let value: i32 = 42;

html! {
    match value {
        x if x > 10 => <p>{"Big"}</p>,
        x if x > 0 => <p>{"Small"}</p>,
        _ => <p>{"Non-positive"}</p>,
    }
};

Let bindings

Braced arm bodies support let bindings and multiple children:

use yew::prelude::*;

html! {
    match data {
        Some(item) => {
            let label = format!("Item: {}", item.name);
            let class = if item.important { "highlight" } else { "normal" };
            <p class={class}>{label}</p>
        }
        None => <p>{"No data"}</p>,
    }
};

Arms with a single element can omit braces. Arms with multiple children or let bindings require braces.

match supports all standard Rust patterns including OR-patterns (A | B), destructuring, and if guards. Exhaustiveness is checked by the Rust compiler.

Loops inside if/match bodies

for, while, and loop inside an if/else if/else/match-arm body follow the same rules they do at the top level of html!, with one caveat: if the loop body is fully Rust-parseable (no html elements anywhere inside), the macro takes the loop as a Rust statement instead of html-control-flow.

The most common way to hit this is a loop whose only child is a bare {expr} block:

// Compiles. The for is at the top level, parsed as html-`for`.
html! {
    for _ in 0..9 {
        {my_foo}
    }
}

// Does NOT compile. The for is inside an `if`, parsed as a Rust statement;
// rustc then complains that the body returns a value where `()` is expected.
html! {
    if condition {
        for _ in 0..9 {
            {my_foo}
        }
    }
}

Wrap the child in an html element to keep it as html-for:

html! {
    if condition {
        for _ in 0..9 {
            <span>{my_foo}</span>
        }
    }
}

See Lists for the full set of workarounds.