JavaScript数组范围问题 [英] Javascript Array Scope Issue

问题描述

解决 - 这个例子code的工作，所以我将它比作非工作我有发现不一致。

SOLVED - This example code worked, so I compared it to the non-working I had and found a discrepancy.

在我的code，一个声明的颜色数组我忘了前添加一个变种的时候，没有工作。

In my code, the one that did not work, when declaring the color array I forgot to add a "var" before it.

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;

就是这样。未产生错误，我想这创造了它由所有粒子共享的全局数组。

That's it. No error was generated and I guess it created it as a global array shared by all the particles.

感谢您的答案大家。我会用它们来写出更好的JavaScript的code。

Thanks for the answers everyone. I will use them to write better javascript code.

老问题（它不再是相关的）是如下：

Old question (which is no longer relevant) is below:

我有一个JavaScript数组范围这个疯狂的问题。

I have this crazy issue with javascript arrays scope.

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]
    }
}

我然后创建ParticleClass粒子阵列，并吸引他们。

I then create an array of ParticleClass particles and draw them.

如果我创建了一堆颗粒，并尝试绘制在屏幕上，SetRandomColorRGB和DrawParticleRGB的伟大工程。每个粒子都有不同的颜色。

If I create a bunch of particles and try to draw them on the screen, SetRandomColorRGB and DrawParticleRGB works great. Each particle has a different color.

如果我用SetRandomColorArray和DrawParticleArray，所有的粒子具有相同的颜色。每一个新粒子产生的时候，所有的粒子变成最后一种颜色SetRandomColorArray回升。

If I use SetRandomColorArray and DrawParticleArray, all the particles have the same color. Each time a new particle is created, all the particles change to the last color SetRandomColorArray picked.

在我看来，数组共享内存，而其他变量则没有。这是真的？这是JavaScript的一个怪癖？别的东西怎么回事？

It looks to me that arrays share memory, whereas other variables do not. Is this true? Is this a quirk of Javascript? Is something else going on?

感谢。

推荐答案

在这里...这可能有助于解释为什么它正在发生：

here... this may help explain why it is happening :

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

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