Javascript：为什么这个实例变量没有定义？

我是Javascript新手，我正在玩WebGL，发现了一个错误，

“self.starshipVertexPositionBuffer未定义”

。在尝试访问itemSize属性时，它看起来像是崩溃了（请参见下面的注释），但在该语句发出之前它正在初始化（请参见下面的注释），所以我不理解为什么会出现该错误。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();
    }

---

非常感谢你的智慧

在代码中的任何地方都不定义

self

。你可能会把它和我搞混了