变量需要先声明才能使用吗?

Question

portName  不存在
没有一个叫portName   string的 id 的images
把你的protname alert 出来看看有咩有问题

Answer 1

js不需要声明变量，不声明会当全局变量来用，但Array那些就得声明类型。你的代码都不完整，slot_Num、slot_PortState估计是这些代码之间有错而使获取不了正确的名称吧。

Answer 2

那没有 id叫 port10101 的图片呢 

Answer 3

我完整的代码是这样的：function initNpc_UMHF_GEI_X_4EF(slot_Num,card_Type)
{
    var portNum=4;
    for(var i=0;i<portNum;i++)
    {
        var portName="";
        var portName1="";
        portName="port"+(10000+(100*(slot_Num+1))+(i+1));
        alert(portName);
        switch (slot_PortState[slot_Num+1][i])
        {
            case 0:
            window.document.images[portName].src=image_fiber[0].src;
            break;
            case 1:
            window.document.images[portName].src=image_fiber[1].src;
            break;
            case 2:
            window.document.images[portName].src=image_fiber[2].src;
            break;
            default:
            window.alert("Error:cardType "+card_Type+",slot "+(slot_Num+1)+",port "+(i+1)+"!");
            break;
        }
    }
}
这是别人的源代码，没问题：function initNpc_GEI_24EC(slot_Num,card_Type)
{
    var portNum=24;
    for(var i=0;i<(portNum-4);i++)
    {
        var portName="";
        portName="port"+(10000+(100*(slot_Num+1))+(i+1));        if((i%2)==0)
        {
            switch (slot_PortState[slot_Num+1][i])
            {
                case 0:
                window.document.images[portName].src=image_copper[3].src;
                break;
                case 1:
                window.document.images[portName].src=image_copper[4].src;
                break;
                case 2:
                window.document.images[portName].src=image_copper[5].src;
                break;
                default:
                window.alert("Error:cardType "+card_Type+",slot "+(slot_Num+1)+",port "+(i+1)+"!");
                break;
            }
        }
        else
        {
            switch (slot_PortState[slot_Num+1][i])
            {
                case 0:
                window.document.images[portName].src=image_copper[0].src;
                break;
                case 1:
                window.document.images[portName].src=image_copper[1].src;
                break;
                case 2:
                window.document.images[portName].src=image_copper[2].src;
                break;
                default:
                window.alert("Error:cardType "+card_Type+",slot "+(slot_Num+1)+",port "+(i+1)+"!");
                break;
            }
        }
    }    for(var i=(portNum-4);i<portNum;i++)
    {
        var portName="";
        var portName1="";
        portName="port"+(10000+(100*(slot_Num+1))+(i+1));
        portName1="port"+(20000+(100*(slot_Num+1))+(i+1));        if((i%2)==0)
        {
            switch (slot_PortState[slot_Num+1][i])
            {
                case 0:
                window.document.images[portName].src=image_copper[3].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 1:
                window.document.images[portName].src=image_copper[4].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 2:
                window.document.images[portName].src=image_copper[5].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 3:
                window.document.images[portName].src=image_copper[3].src;
                window.document.images[portName1].src=image_fiber[1].src;
                break;
                case 4:
                window.document.images[portName].src=image_copper[3].src;
                window.document.images[portName1].src=image_fiber[2].src;
                break;
                default:
                window.alert("Error:cardType "+card_Type+",slot "+(slot_Num+1)+",port "+(i+1)+"!");
                break;
            }
        }
        else
        {
            switch (slot_PortState[slot_Num+1][i])
            {
                case 0:
                window.document.images[portName].src=image_copper[0].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 1:
                window.document.images[portName].src=image_copper[1].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 2:
                window.document.images[portName].src=image_copper[2].src;
                window.document.images[portName1].src=image_fiber[0].src;
                break;
                case 3:
                window.document.images[portName].src=image_copper[0].src;
                window.document.images[portName1].src=image_fiber[1].src;
                break;
                case 4:
                window.document.images[portName].src=image_copper[0].src;
                window.document.images[portName1].src=image_fiber[2].src;
                break;
                default:
                window.alert("Error:cardType "+card_Type+",slot "+(slot_Num+1)+",port "+(i+1)+"!");
                break;
            }
        }
    }
}

Answer 4

firefox + firebug 看看在哪错

Answer 5

'window.document.images[...]'为空或不是对象
都已经提示了，就是window.document.images[...]不存在，所以不能再“.src”