node.js - Nodejs报错Cannot read property 'call' of undefined

Question

Write this in the middleware:
wechat.reply.call(this);
Write the reply function in wechat like this:

Wechat.prototype.reply = function(){
    console.log('bbbbb');
    var content = this.body;
    var message = this.weixin;
    var xml = util.tpl(content,message)

    console.log(xml);
    this.status = 200
    this.type = 'application/xml'
    this.body = xml
    return
}

Then an error is reported

TypeError: Cannot read property 'call' of undefined
      at Object.<anonymous> (C:\www\koa\wechat\wechat\g.js:54:16)
      at Generator.next (<anonymous>)
      at onFulfilled (C:\www\koa\wechat\node_modules\co\index.js:65:19)
      at process._tickCallback (internal/process/next_tick.js:109:7)
      

By the way, isn’t the call function available in native js? Why did I get an error when I called it?

Moreover, after searching on Baidu, there are very few people with this error...
Ask the master: When does this error usually occur? What is the reason for the error?

Answer 1

For example, a.call(this,null), but at this time a is undefined, the error you encountered will be reported
Have you confirmed that there is a wechat.apply method?

Answer 2

Writing like this in the middleware:
wechat.reply.call(this); writing the reply function in wechat like this:

The wechat instance should have no value, please print it before calling.

console.log(wechat.reply)

Answer 3

If x in x.call is not defined, the .call under it cannot be accessed, so you should first make sure whether wechat.reply has been defined.
Also, note that in JS, variable names are case-sensitive.