使用Array.find时如何避免丢失this指向？

你遇到的报错是因为：将History方法作为commands数组对象的method属性存储后，调用该方法时，this的指向不再是类实例，而是指向了commands里的单个command对象，自然无法访问类的status属性。

方法1：定义时绑定this #

在commands数组中，用bind把类实例的this绑定到History方法上，确保方法执行时this始终指向类实例：

module.exports = new class {
   status = { COMMAND_SUCCESS: 1 }

   commands = [{
        name: "history",
        method: this.History.bind(this) // 绑定类实例的this
   }];

   commandsNames = ["history"];

   async Execute(command)
   {
        var commandParts = command.toLowerCase().split(" ");
        var commandFound = this.commands.find(command => command.name === commandParts[0]);
        return commandFound["method"]();
   }

   async History()
   {
      return this.status.COMMAND_SUCCESS; 
   }
}

方法2：用箭头函数定义类方法 #

箭头函数的this遵循词法作用域，会自动继承外层类实例的this，无需额外绑定：

module.exports = new class {
   status = { COMMAND_SUCCESS: 1 }

   commands = [{
        name: "history",
        method: this.History
   }];

   commandsNames = ["history"];

   async Execute(command)
   {
        var commandParts = command.toLowerCase().split(" ");
        var commandFound = this.commands.find(command => command.name === commandParts[0]);
        return commandFound["method"]();
   }

   // 改为箭头函数形式
   History = async () => {
      return this.status.COMMAND_SUCCESS; 
   }
}

方法3：调用方法时绑定this #

在Execute方法中调用method时，用call把当前类实例的this传入，强制指定方法的this指向：

module.exports = new class {
   status = { COMMAND_SUCCESS: 1 }

   commands = [{
        name: "history",
        method: this.History
   }];

   commandsNames = ["history"];

   async Execute(command)
   {
        var commandParts = command.toLowerCase().split(" ");
        var commandFound = this.commands.find(command => command.name === commandParts[0]);
        // 调用时用call绑定类实例的this
        return commandFound["method"].call(this);
   }

   async History()
   {
      return this.status.COMMAND_SUCCESS; 
   }
}

内容的提问来源于stack exchange，提问作者user13933916