JavaScript (node.js) 变量在内部函数调用时无法访问。 now.js

发布于 2024-11-26 01:25:48 字数 376 浏览 0 评论 0原文

我在节点项目中使用 now.js 和 Mongoose，并且在访问 mongoose 函数内的 this.now 对象时遇到问题。例如

everyone.now.joinDoc = function (project_id){  
  this.now.talk(); //this will work
  Project.findOne({'_id':project_id}, function(err, project){
    if(project){
      this.now.talk(); // this will not work "TypeError: Cannot call method 'bark' of undefined"
    };
  });
};

原文

I am using now.js and Mongoose in a node project and am having trouble accessing the this.now object inside of a mongoose function. E.g.

everyone.now.joinDoc = function (project_id){  
  this.now.talk(); //this will work
  Project.findOne({'_id':project_id}, function(err, project){
    if(project){
      this.now.talk(); // this will not work "TypeError: Cannot call method 'bark' of undefined"
    };
  });
};

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李白 2024-12-03 01:25:48

将代码更改为：

everyone.now.joinDoc = function (project_id){  
  this.now.talk();  // this will work
  var that = this;  // save 'this' to something else so it will be available when 'this' has been changed
  Project.findOne({'_id':project_id}, function(err, project){
    if(project){
      that.now.talk();  // use local variable 'that' which hasn't been changed
    };
  });
};

在您的内部函数中，this 可能被设置为其他内容。因此，为了保留您想要访问的值，您可以将其分配给内部函数中可用的不同局部变量。

Change the code to this:

everyone.now.joinDoc = function (project_id){  
  this.now.talk();  // this will work
  var that = this;  // save 'this' to something else so it will be available when 'this' has been changed
  Project.findOne({'_id':project_id}, function(err, project){
    if(project){
      that.now.talk();  // use local variable 'that' which hasn't been changed
    };
  });
};

Inside your inner function, the this is probably being set to something else. So, to preserve the value you want to access, you assign it to a different local variable that will be available in the inner function.

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〃温暖了心ぐ 2024-12-03 01:25:48

everyone.now.joinDoc = function (project_id){  
  this.now.talk();  // this will work
  Project.findOne({'_id':project_id}, (function(tunnel, err, project){
    if(project){
      this.now.talk(); 
    };
  }).bind(this, "tunnel")); // overwrite `this` in callback to refer to correct `this`
};

使用Function.prototype.bind将this的值设置为你想要的值

everyone.now.joinDoc = function (project_id){  
  this.now.talk();  // this will work
  Project.findOne({'_id':project_id}, (function(tunnel, err, project){
    if(project){
      this.now.talk(); 
    };
  }).bind(this, "tunnel")); // overwrite `this` in callback to refer to correct `this`
};

Use Function.prototype.bind to set the value of this to the value you want

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