在使用.map

Question

我有以下课程：

class RegisterUser {
  constructor(username, password, ispublic){
    this.username = username;
    this.password = password;
    this.ispublic = ispublic;
    this.identity = crypto.signKey();
    this.preKeys = [];
    if (ispublic){
      this.preKeys = crypto.getPreKeys(10);
    }
  }
  get data(){
    return {
      identity_key: this.identity.publicKey,
      username: this.username,
      usernameSignature: this.usernameSignature,
      signedPreKeys: this.signedPreKeys,
      ispublic: this.ispublic
    }
  }
  get usernameSignature(){
    return this.identity.sign(buf(this.username, 'utf8'));
  }
  signPreKey(key){
    var publicKey = key.publicKey;
    var signature = this.identity.sign(pub);
    return {
      publicKey: publicKey,
      signature: signature
    }
  }
  get signedPreKeys(){
    var signFunc = this.signPreKey;
    return this.preKeys ? this.preKeys.map(signFunc) : null;
  }
  get encryptedIdentity(){
    var cipher = ncrypto.createCipher('aes192', this.password);
    var encrypted = new Buffer(cipher.update(this.identity.secretKey));
    return Buffer.concat([encrypted, new Buffer(cipher.final())]);
  }
}

在这个类的新实例化实例上调用.data()时，我得到：

  

无法在signPreKey函数中读取未定义的属性'identity'。

有没有办法以不会取代.map的方式使用this？

Answer 1

您可以使用bind()来强制功能的上下文。

  get signedPreKeys(){
    var signFunc = this.signPreKey.bind(this);
    return this.preKeys ? this.preKeys.map(signFunc) : null;
  }

或者，将this作为第二个参数传递给map()：

  get signedPreKeys(){
    var signFunc = this.signPreKey;
    return this.preKeys ? this.preKeys.map(signFunc, this) : null;
  }

Answer 2

当然，数组map方法完全为此目的采用第二个参数。

来自MDN：

var new_array = arr.map(callback[, thisArg])

只需传递你想要的thisArg作为第二个参数：

return this.preKeys ? this.preKeys.map(signFunc, this) : null;