'this.randomGenes'不是一个函数吗？

Question

所以我对这个p5js脚本有点麻烦。我得到一个TypeError，说“this.randomGenes不是一个函数”，但它看起来像一个我......我不明白错误来自哪里。它的拼写都是正确的，所有的分号都在那里，所有的括号都是关闭的，所有的括号都是。这个错误根本不会在我身上突出。

function DNA(genes) { 
    this.maxWeight = 25; 
    this.maxSpeed = 25; 

    if (genes) { 
     this.genes = genes; 
    } else { 
     this.genes = []; // weight, position, maxspeed, rgba 
     this.randomGenes(); 
    } 

    this.randomGenes = function() { 
     this.genes[0] = random(this.maxWeight); 
     this.genes[1] = [random(height), random(width)]; 
     this.genes[2] = random(this.maxSpeed); 
     this.genes[3] = [random(255), random(255), random(255), random(255)]; 
    } 
} 

Answer 1

你需要让你的DNA功能的“实例”，以便this绑到一个对象实例，然后你可以从实例调用randomGenes。如果您只运行DNA函数，则this将被错误绑定，并且不会找到该函数。

function DNA(genes) { 
 
    this.maxWeight = 25; 
 
    this.maxSpeed = 25; 
 

 
    if (genes) { 
 
     this.genes = genes; 
 
    } else { 
 
     this.genes = []; // weight, position, maxspeed, rgba 
 
     this.randomGenes(); 
 
    } 
 

 
    this.randomGenes = function() { 
 
     this.genes[0] = random(this.maxWeight); 
 
     this.genes[1] = [random(height), random(width)]; 
 
     this.genes[2] = random(this.maxSpeed); 
 
     this.genes[3] = [random(255), random(255), random(255), random(255)]; 
 
    } 
 
} 
 

 
// Make an instance of the DNA object so that `this` gets bound to it 
 
var DNA1 = new DNA("myGenes"); 
 

 
// Now, you can call the function via the instance 
 
// Here, this will cause an error about "random" not being defined, but 
 
// that actually proves that "randomGenes" was invoked. 
 
DNA1.randomGenes();

现在，在评论@qqilihq提到的，如果没有传递任何参数，创建您的实例，你会得到你的错误，因为你正试图调用函数它已经前作为方法分配。为了纠正这个问题，我们需要修改代码，但是同样的修改也会出于另一个原因...

当你创建一个函数的新实例时，函数被称为“函数构造函数”，因为你调用它来构造对象实例。由于（通常）对象的所有实例都使用相同的行为（方法），我们通常将这些方法添加到所有实例将继承的对象的基础“原型”对象。这样你只需要存储一次函数，所有的实例都会继承它。通过将你的函数移动到原型中，它在任何实例被实现之前都在内存中，因此不仅解决了你的问题，而且也更加高效。

所以，你的代码真的应该是：

function DNA(genes) { 
 
     // Instance properties get created using the "this" keyword 
 
     // inside the constructor function 
 
     this.maxWeight = 25; 
 
     this.maxSpeed = 25; 
 

 
     if (genes) { 
 
      this.genes = genes; 
 
     } else { 
 
      this.genes = []; // weight, position, maxspeed, rgba 
 
      this.randomGenes(); 
 
     } 
 
    } 
 
    
 
    // By adding the function to the prototype of DNA, all instances constructed 
 
    // via the DNA constructor function will inherit the method: 
 
    DNA.prototype.randomGenes = function() { 
 
      this.genes[0] = random(this.maxWeight); 
 
      this.genes[1] = [random(height), random(width)]; 
 
      this.genes[2] = random(this.maxSpeed); 
 
      this.genes[3] = [random(255), random(255), random(255), random(255)]; 
 
    } 
 

 
    // Make an instance of the DNA object so that `this` gets bound to it 
 
    var DNA1 = new DNA(); 
 

 
    // Now, you can call the function via the instance 
 
    // Here, this will cause an error about "random" not being defined, but 
 
    // that actually proves that "randomGenes" was invoked. 
 
    DNA1.randomGenes();