'this.randomGenes'不是一個函數嗎？

Question

所以我對這個p5js腳本有點麻煩。我得到一個TypeError，說「this.randomGenes不是一個函數」，但它看起來像一個我......我不明白錯誤來自哪裏。它的拼寫都是正確的，所有的分號都在那裏，所有的括號都是關閉的，所有的括號都是。這個錯誤根本不會在我身上突出。

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

你需要讓你的DNA功能的「實例」，以便this綁到一個對象實例，然後你可以從實例調用randomGenes。如果您只運行DNA函數，則this將被錯誤綁定，並且不會找到該函數。

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();

現在，在評論@qqilihq提到的，如果沒有傳遞任何參數，創建您的實例，你會得到你的錯誤，因爲你正試圖調用函數它已經前作爲方法分配。爲了糾正這個問題，我們需要修改代碼，但是同樣的修改也會出於另一個原因...

當你創建一個函數的新實例時，函數被稱爲「函數構造函數」，因爲你調用它來構造對象實例。由於（通常）對象的所有實例都使用相同的行爲（方法），我們通常將這些方法添加到所有實例將繼承的對象的基礎「原型」對象。這樣你只需要存儲一次函數，所有的實例都會繼承它。通過將你的函數移動到原型中，它在任何實例被實現之前都在內存中，因此不僅解決了你的問題，而且也更加高效。

所以，你的代碼真的應該是：

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();