Javascript：爲什麼這個實例變量未定義？

Question

我是Javascript新手，我正在玩弄WebGL並得到錯誤，"self.starshipVertexPositionBuffer is undefined"。它在嘗試訪問itemSize屬性時看起來像是崩潰了（見下面的註釋），但是在語句創建之前它正在被初始化（見下面的註釋），所以我不明白爲什麼它會崩潰。你的想法？

var starship; 
    function initstarship() 
    { 
     starship = new starship(); 
     starship.initBuffers(); 
    } 

    function starship() 
    { 
     this.angle = 0; 
     this.speed = 0; 
     this.xDir = 0; 
     this.yDir = 0; 
     this.xPos = 0.0; 
     this.yPos = 0.0; 
     this.starshipVertexPositionBuffer = null; 
     this.starshipVertexTextureCoordBuffer = null; 
     this.starshipVertexIndexBuffer = null; 
    } 

    starship.prototype.updatePosition = function(timeElapsed){ 
     this.xPos += this.xDir * this.speed; 
     this.yPos += this.yDir * this.speed; 
    } 

    starship.prototype.initBuffers = function() { 
     this.starshipVertexPositionBuffer = gl.createBuffer(); 
     gl.bindBuffer(gl.ARRAY_BUFFER, this.starshipVertexPositionBuffer); 
     vertices = [ 
      -0.15, -0.15, 0.15, 
      0.15, -0.15, 0.15, 
      0.15, 0.15, 0.15, 
      -0.15, 0.15, 0.15, 

     ]; 
     gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); 

     //INITIALIZED HERE 
     this.starshipVertexPositionBuffer.itemSize = 3; 
     this.starshipVertexPositionBuffer.numItems = 4; 

     this.starshipVertexTextureCoordBuffer = gl.createBuffer(); 
     gl.bindBuffer(gl.ARRAY_BUFFER, this.starshipVertexTextureCoordBuffer); 
     var textureCoords = [ 
      0.0, 0.0, 
      1.0, 0.0, 
      1.0, 1.0, 
      0.0, 1.0, 

     ]; 
     gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), gl.STATIC_DRAW); 
     this.starshipVertexTextureCoordBuffer.itemSize = 2; 
     this.starshipVertexTextureCoordBuffer.numItems = 4; 

     this.starshipVertexIndexBuffer = gl.createBuffer(); 
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.starshipVertexIndexBuffer); 
     var starshipVertexIndices = [ 
      0, 1, 2,  0, 2, 3,  
     ] 
     gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(starshipVertexIndices), gl.STATIC_DRAW); 
     this.starshipVertexIndexBuffer.itemSize = 1; 
     this.starshipVertexIndexBuffer.numItems = 6; 
    } 

    starship.prototype.draw = function() 
    {  
     mvPushMatrix(); 

     mat4.translate(mvMatrix, [this.xPos, this.yPos, z]); 

     mat4.rotate(mvMatrix, degToRad(this.angle), [0, 0, 1]); 

     gl.bindBuffer(gl.ARRAY_BUFFER, self.starshipVertexPositionBuffer); 

     //CRASHING ON THIS NEXT LINE 
     gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, self.starshipVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0); 

     gl.bindBuffer(gl.ARRAY_BUFFER, self.starshipVertexTextureCoordBuffer); 
     gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, self.starshipVertexTextureCoordBuffer.itemSize, gl.FLOAT, false, 0, 0); 

     gl.activeTexture(gl.TEXTURE0); 
     gl.bindTexture(gl.TEXTURE_2D, starshipTexture); 
     gl.uniform1i(shaderProgram.samplerUniform, 0); 

     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, self.starshipVertexIndexBuffer); 
     setMatrixUniforms(); 
     gl.drawElements(gl.TRIANGLES, self.starshipVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0); 

     mvPopMatrix(); 
    } 

    function webGLStart() { 
     initstarship(); 
     tick(); 
    } 

非常感謝您的智慧！

Answer 1

您沒有在該代碼中的任何位置定義self。您可能會將其與this混淆。