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 // 发布订阅
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class EventEmitter {
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  constructor() {
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    this.cache = {}
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  }
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  // 订阅事件
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  on(name, callback, once = false) {
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    if (!this.cache[name]) {
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      this.cache[name] = []
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    }
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    this.cache[name].push({
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      callback,
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      once
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    })
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  }
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  // 只订阅一次
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  once(name, callback) {
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    this.on(name, callback, true)
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  }
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  // 发布
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  emit(name, ...rest) {
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    if (!this.cache[name]) {
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      return
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    }
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    this.cache[name].forEach((param, index) => {
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      const { once, callback } = param;
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      if (once) {
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        this.cache[name].splice(index, 1);
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        if (!this.cache[name]?.length) delete this.cache[name]
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      }
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      callback.call(this, ...rest)
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    })
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  }
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  // 取消订阅
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  off(name, callback) {
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    if (!name) { this.cache = {}; return; }
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    if (!callback) { delete this.cache[name]; return }
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    if (!this.cache[name]) { return }
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    const i = this.cache[name].findIndex((f) => f.callback === callback)
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    this.cache[name].splice(i, 1);
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    if (!this.cache[name].length) delete this.cache[name]
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  }
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}