Javascript数组作用域问题

已解决-此示例代码有效，因此我将其与未工作的代码进行了比较，发现了差异

在我的代码中，一个不起作用的代码，当声明颜色数组时，我忘记在它前面添加一个“var”

m_color = [];
m_color[0] = 255;
m_color[1] = 255;
m_color[2] = 255;
m_color[3] = 255;

而不是：

var m_color = [];
m_color[0] = 255;
m_color[1] = 255;
m_color[2] = 255;
m_color[3] = 255;

就这样。没有生成错误，我猜它创建了一个由所有粒子共享的全局数组

谢谢大家的回答。我将使用它们来编写更好的javascript代码

旧问题（不再相关）如下：

---

我对javascript数组的作用域有一个疯狂的问题

我有一个类粒子：

function ParticleClass()
{
    var m_color = [];
    m_color[0] = 255;
    m_color[1] = 255;
    m_color[2] = 255;
    m_color[3] = 255;

    var m_red = 255;
    var m_green = 255;
    var m_blue = 255;

    this.SetRandomColorRGB = SetRandomColorRGB;
    this.SetRandomColorArray = SetRandomColorArray;
    this.DrawParticleRGB = DrawParticleRGB;
    this.DrawParticleArray = DrawParticleArray;

    function SetRandomColorRGB()
    {
        m_red = Math.floor( Math.random() * 255 );
        m_green = Math.floor( Math.random() * 255 );
        m_blue = Math.floor( Math.random() * 255 );
    }

    function SetRandomColorArray()
    {
        m_color[0] = Math.floor( Math.random() * 255 );
        m_color[1] = Math.floor( Math.random() * 255 );
        m_color[2] = Math.floor( Math.random() * 255 );
    }

    function DrawParticleRGB( ctx )
    {
        // I draw the particle using m_red, m_green and m_blue.
    }

    function DrawParticleArray( ctx )
    {
        // I draw the particle using m_color[0], m_color[1], m_color[2]
    }
}

然后我创建一个ParticleClass粒子数组并绘制它们

如果我创建一组粒子并尝试在屏幕上绘制它们，SetRandomColorRGB和DrawParticleRGB效果很好。每个粒子都有不同的颜色

如果使用SetRandomColorArray和DrawParticleArray，则所有粒子都具有相同的颜色。每次创建新粒子时，所有粒子都会更改为上次拾取的颜色集RandomColorArray

在我看来，数组共享内存，而其他变量则不共享。这是真的吗？这是Javascript的一个怪癖吗？还有别的事吗

---

谢谢。

变量的作用域在函数ParticleClass（）中。因此，在此空间中定义的函数中的变量将与其父函数共享作用域

这就是为什么有时候会在Javascript中看到这种模式-

var self = this;
$('.someClass').each(function(i) {
   // function is defined as a closure
   // but it shares its scope with its parent so it can see self and access the parent's  
   // pointer to this.
});

为什么不使用prototype来定义函数

例如

这将为您获得所需的命名空间

---

这里有一个例子：

这样做并没有问题，但话说回来，你们这样做让生活变得更加困难；最好正确使用原型：

function ParticleClass()
{
    this.m_color = [255, 255, 255, 255];

    this.m_red = 255;
    this.m_green = 255;
    this.m_blue = 255;
}

(function(p) {

p.SetRandomColorRGB = function () {
        this.m_red = Math.floor( Math.random() * 255 );
        this.m_green = Math.floor( Math.random() * 255 );
        this.m_blue = Math.floor( Math.random() * 255 );
}

p.SetRandomColorArray = function () {
        this.m_color[0] = Math.floor( Math.random() * 255 );
        this.m_color[1] = Math.floor( Math.random() * 255 );
        this.m_color[2] = Math.floor( Math.random() * 255 );
}

p.DrawParticleRGB = function( ctx ) {
        // I draw the particle using m_red, m_green and m_blue.
}

p.DrawParticleArray = function( ctx )
{
        // I draw the particle using m_color[0], m_color[1], m_color[2]
}

}(ParticleClass.prototype);

---

这里。。。这可能有助于解释为什么会发生这种情况：

var data             = {};               // create a  data object 
data.string          = "hey society";    // Add a string value property
data.num             = 0;                // Add a integer value property
data.arr             = [0,1,2];          // Add an array property
data.date            = new Date();       // Add an object property

                     // here is where the fun starts! 

// Create a var for string property

var sString          = data.string;      // sets to "hey society", as expected.. cool
data.string          = "changed"         // change the value and the compare :
data.string         == sString           // returns false, the values are different

                      // same happens for a number.

// Now lets copy this array
var oArr             = data.arr;         // (seeing the comment pattern? XD)
data.arr             .push(3);           // and modify it.
data.arr            == oArr              // should be false? Nope. returns true.
                                         // arrays are passed by reference.

var oDate            = data.date           // what about objects?       
data.date            .setHours(0);         // modify the variable and
oDate.getTime()     == data.date.getTime() // it returns true, too!

                      // so, how do we fix the array problem?

// right in front of yer nose
var oArrFix          = data.arr.splice(0) // get a new array based on 
data.arr             .push(4)             // an unmodified version of the original
data.arr            == oArrFix            // false.. huh..

                     // How do we use this as a fix

data.arr["changed"] == false;

oArrFix              = ChangeOriginalArray( data.arr );

// When you are expecting an array..
function ChangeOriginalArray( arr )       // pass as a parameter
{
    var aArr = arr.splice(0);             // make a copy!

    if (aArr["changed"] == false)         // check has same value!
    {
        aArr["newKey"]   = "newVal";      // add a value

        arr["changed"]   = true;          // change original value
    }

    return aArr;
}

oArrFix["newKey"]       == data.arr["newKey"] // false
oArrFix["changed"]      == true               // no, created
data.arr["changed"]     == oArrFix["changed"] // nah, passed by value, not reference

---

这不应该发生，我很确定不会发生。每个粒子应具有不同的阵列。你能提供一个你的代码的工作演示，这样我们就可以确切地知道出了什么问题吗？你确定它没有抛出任何错误吗<代码>this.DrawParticleRGB=DrawParticleRGB不应该是this.DrawParticleRGB=DrawParticleWithRGB

SetRandomColorRGB（）

和

SetRandomColorArray（）

执行完全相同的操作，减去赋值的位置。就个人而言，我会在函数中添加

this.m_red

等，但这是一种风格选择。问题必须在绘图函数中，除非代码中有错误（使用某种调试器捕捉任何警告或错误）。这不是确切的代码。我的代码中有更多的东西，所以我写了这个简单的版本。这就是为什么函数名是错误的。我将尝试创建一个JSFIDLE示例。

var data             = {};               // create a  data object 
data.string          = "hey society";    // Add a string value property
data.num             = 0;                // Add a integer value property
data.arr             = [0,1,2];          // Add an array property
data.date            = new Date();       // Add an object property

                     // here is where the fun starts! 

// Create a var for string property

var sString          = data.string;      // sets to "hey society", as expected.. cool
data.string          = "changed"         // change the value and the compare :
data.string         == sString           // returns false, the values are different

                      // same happens for a number.

// Now lets copy this array
var oArr             = data.arr;         // (seeing the comment pattern? XD)
data.arr             .push(3);           // and modify it.
data.arr            == oArr              // should be false? Nope. returns true.
                                         // arrays are passed by reference.

var oDate            = data.date           // what about objects?       
data.date            .setHours(0);         // modify the variable and
oDate.getTime()     == data.date.getTime() // it returns true, too!

                      // so, how do we fix the array problem?

// right in front of yer nose
var oArrFix          = data.arr.splice(0) // get a new array based on 
data.arr             .push(4)             // an unmodified version of the original
data.arr            == oArrFix            // false.. huh..

                     // How do we use this as a fix

data.arr["changed"] == false;

oArrFix              = ChangeOriginalArray( data.arr );

// When you are expecting an array..
function ChangeOriginalArray( arr )       // pass as a parameter
{
    var aArr = arr.splice(0);             // make a copy!

    if (aArr["changed"] == false)         // check has same value!
    {
        aArr["newKey"]   = "newVal";      // add a value

        arr["changed"]   = true;          // change original value
    }

    return aArr;
}

oArrFix["newKey"]       == data.arr["newKey"] // false
oArrFix["changed"]      == true               // no, created
data.arr["changed"]     == oArrFix["changed"] // nah, passed by value, not reference