Javascript 使用Dynamic在画布上添加更多图像

我正在制作一个应用程序，但我遇到了问题。我需要在按下按钮时在画布上添加新的点图像。下面是一个代码：

var ID = 0;
var points = [];

function addPoint(){
points.push({id: ID, posX: 0, posY: 0, url: "img/point.png"});
ID++;
showPoints();
}

function showPoints(){
var img = new Array();
var point = new Array();
var stage = new Kinetic.Stage({
    container: 'cvsCroatia',
    width: 574,
    height: 508
});
var layer = new Kinetic.Layer();

for(var j=0; j < ID; j++){
    img[j] = new Image();
    img[j].src = 'img/point.png';
    img[j].onload = (function(){
        point[j] = new Kinetic.Image({
            x: points[j].posX,
            y: points[j].posY,
            image: img[j],
            width: 13,
            height: 13,
            name:  img[j],
            draggable: true
        });
    });
    layer.add(point[j]);

}   
stage.add(layer);
}

但我有一个错误：

未捕获的TypeError:无法设置未定义的Dynamic-v4.4.0.min.js:29的属性“索引”

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你知道怎么回事吗？谢谢你的回答。艾伦

谢谢你的回答，我把所有变量都放在了全局范围内，但不幸的是得到了同样的错误

var img = new Array(); // the simplest solution is to make img visible outside your function
function showPoints(){
    // var img = new Array();        // HERE img is a LOCAL variable, only visible to the showPoints() function
    var point = new Array();        
    var stage = new Kinetic.Stage({
    container: 'cvsCroatia',
    width: 574,
    height: 508
});

 var ID = 0;
 var points = [];

 var img = new Array();
 var point = new Array();

 function showPoints(){
var stage = new Kinetic.Stage({
    container: 'cvsCroatia',
    width: 574,
    height: 508
});
var layer = new Kinetic.Layer();

for(var j=0; j < ID; j++){
    img[j] = new Image();
    img[j].src = 'img/point.png';
    img[j].onload = (function(){
        point[j] = new Kinetic.Image({
            x: points[j].posX,
            y: points[j].posY,
            image: img[j],
            width: 13,
            height: 13,
            name:  img[j],
            draggable: true
        });
    });
    layer.add(point[j]);

}   
stage.add(layer);
 }

  function addPoint(){
points.push({id: ID, posX: 0, posY: 0, url: "img/point.png"});
ID++;
showPoints();
}

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实际上，您应该将此函数中的所有内容都设置为全局范围