使用 `char` 类型

查看完整源代码 或 在线查看编译后的示例

`#[wasm_bindgen]` 宏将 rust `char` 类型转换为单个代码点的 js `string`，本示例展示了如何使用它。

打开本示例应该会显示一个带有随机字符作为其 `key` 和 0 作为其 `count` 的计数器。您可以点击 `+` 按钮增加计数器的计数。通过点击“添加计数器”按钮，您应该会看到一个新的计数器被添加到列表中，它使用不同的随机字符作为其 `key`。

在幕后，javascript 从一个字符数组中选择一个随机字符，并将其传递给 rust Counter 结构的构造函数，因此您在页面上看到的字符已经从 js 到 rust，再从 rust 回到 js 完成了完整的往返过程。

src/lib.rs

#![allow(unused)]
fn main() {
use wasm_bindgen::prelude::*;

// lifted from the `console_log` example
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_namespace = console)]
    fn log(s: &str);
}

#[wasm_bindgen]
#[derive(Debug)]
pub struct Counter {
    key: char,
    count: i32,
}

#[wasm_bindgen]
impl Counter {
    pub fn new(key: char, count: i32) -> Counter {
        log(&format!("Counter::new({}, {})", key, count));
        Counter { key, count }
    }

    pub fn key(&self) -> char {
        log("Counter.key()");
        self.key
    }

    pub fn count(&self) -> i32 {
        log("Counter.count");
        self.count
    }

    pub fn increment(&mut self) {
        log("Counter.increment");
        self.count += 1;
    }

    pub fn update_key(&mut self, key: char) {
        self.key = key;
    }
}
}

index.js

/* eslint-disable no-unused-vars */
import { chars } from './chars-list.js';
let imp = import('./pkg');
let mod;

let counters = [];
imp
  .then(wasm => {
      mod = wasm;
      addCounter();
      let b = document.getElementById('add-counter');
      if (!b) throw new Error('Unable to find #add-counter');
      b.addEventListener('click', ev => addCounter());
  })
  .catch(console.error);

function addCounter() {
    let ctr = mod.Counter.new(randomChar(), 0);
    counters.push(ctr);
    update();
}

function update() {
    let container = document.getElementById('container');
    if (!container) throw new Error('Unable to find #container in dom');
    while (container.hasChildNodes()) {
        if (container.lastChild.id == 'add-counter') break;
        container.removeChild(container.lastChild);
    }
    for (var i = 0; i < counters.length; i++) {
        let counter = counters[i];
        container.appendChild(newCounter(counter.key(), counter.count(), ev => {
            counter.increment();
            update();
        }));
    }
}

function randomChar() {
    console.log('randomChar');
    let idx = Math.floor(Math.random() * (chars.length - 1));
    console.log('index', idx);
    let ret = chars.splice(idx, 1)[0];
    console.log('char', ret);
    return ret;
}

function newCounter(key, value, cb) {
    let container = document.createElement('div');
    container.setAttribute('class', 'counter');
    let title = document.createElement('h1');
    title.appendChild(document.createTextNode('Counter ' + key));
    container.appendChild(title);
    container.appendChild(newField('Count', value));
    let plus = document.createElement('button');
    plus.setAttribute('type', 'button');
    plus.setAttribute('class', 'plus-button');
    plus.appendChild(document.createTextNode('+'));
    plus.addEventListener('click', cb);
    container.appendChild(plus);
    return container;
}

function newField(key, value) {
    let ret = document.createElement('div');
    ret.setAttribute('class', 'field');
    let name = document.createElement('span');
    name.setAttribute('class', 'name');
    name.appendChild(document.createTextNode(key));
    ret.appendChild(name);
    let val = document.createElement('span');
    val.setAttribute('class', 'value');
    val.appendChild(document.createTextNode(value));
    ret.appendChild(val);
    return ret;
}