JavaScript: 简单减法 returns NaN

Question

我有一个问题，我的碰撞检测功能有时会将实体位置设置为 NaN。当我打开控制台（在 chrome 上）时，实体的位置和碰撞是有效数字，但有时它们会相互减去 returns NaN。

updateCollision = function(entity,rect) {
var a = entity.x - rect.x; // a = NaN , entity.x = 3117.2646499953607 , rect.x = 3296.976967651385
var b = entity.y - rect.y; // b = NaN , entity.y = 3024.105915848102 , rect.y = 3144.4270586199345

if( isNaN(a) ) // isNaN(a) = true
{
    console.log("not again >:("); // but console doesn't log
}

//the code continues but its not important

控制台截图：

所以我真的很困惑，不知道如何处理这个问题。

Answer 1

我需要查看更多你的代码，看看到底哪里出了问题，但 NaN 肯定是对 undefined 类型进行数学运算的结果，所以请仔细查看是否有 [=10] =]

Answer 2

我又重写了一次代码，但我再也没有得到 NaN 值了

固定函数：

updateCollision = function(entity,rect) {
var a = entity.x - rect.x;
var b = entity.y - rect.y;

var unrotatedCircleY = Math.sin((-rect.angle)/180*Math.PI)*a + Math.cos((-rect.angle)/180*Math.PI)*b +rect.y;
var unrotatedCircleX = Math.cos((-rect.angle)/180*Math.PI)*a - Math.sin((-rect.angle)/180*Math.PI)*b +rect.x;
var r = entity.collRad/2;

var closestX, closestY, aX, aY;


if (unrotatedCircleX < rect.x - rect.width/2 )
{
    closestX = rect.x - rect.width/2;
    aX = closestX;
}
else if (unrotatedCircleX  > rect.x + rect.width/2 )
{
    closestX = rect.x + rect.width/2;
    aX = closestX;
}
else
{
    closestX = unrotatedCircleX;
    aX=rect.x;
}

if (unrotatedCircleY < rect.y - rect.height/2 )
{
    closestY = rect.y - rect.height/2;
    aY = closestY;
}
else if (unrotatedCircleY > rect.y + rect.height/2 )
{
    closestY = rect.y + rect.height/2;
    aY = closestY;
}
else
{
    closestY = unrotatedCircleY;
    aY = rect.y;
}


var collision = false;

var distance = getDistance(unrotatedCircleX , unrotatedCircleY, closestX, closestY);
if (distance < r)
collision = true;
else
collision = false;

if( collision && entity.type == "bullet")
{
    entity.hp = 0;
}
else if(collision)
{
    if( entity.type == "bullet")
    {
        DeleteEntity(entity);
        return;
    }
    if( rect.collType == "solid" )
    {

        var positionAngle = Math.atan2( -closestY + unrotatedCircleY , -closestX + unrotatedCircleX );

        var y_vel = Math.sin((-rect.angle)/180*Math.PI)*entity.x_vel + Math.cos((-rect.angle)/180*Math.PI)*entity.y_vel;
        var x_vel = Math.cos((-rect.angle)/180*Math.PI)*entity.x_vel - Math.sin((-rect.angle)/180*Math.PI)*entity.y_vel;

        y_vel *= 0.9;
        x_vel *= 0.9;



        unrotatedCircleX = closestX + Math.cos(positionAngle)*(r);
        unrotatedCircleY = closestY + Math.sin(positionAngle)*(r);

        a = unrotatedCircleX - rect.x;
        b = unrotatedCircleY - rect.y;

        entity.y = Math.sin((rect.angle)/180*Math.PI)*a + Math.cos((rect.angle)/180*Math.PI)*b + rect.y;
        entity.x = Math.cos((rect.angle)/180*Math.PI)*a - Math.sin((rect.angle)/180*Math.PI)*b + rect.x;

        entity.y_vel = Math.sin((rect.angle)/180*Math.PI)*x_vel + Math.cos((rect.angle)/180*Math.PI)*y_vel;
        entity.x_vel = Math.cos((rect.angle)/180*Math.PI)*x_vel - Math.sin((rect.angle)/180*Math.PI)*y_vel;
    }
    if( rect.collType == "trigger" )
    {
        if( level["commandList"][rect.data].command == "tp" )
        {
            entity.x = level["commandList"][rect.data].x;
            entity.y = level["commandList"][rect.data].y;
        }
        if( level["commandList"][rect.data].command == "loadLevel" )
        {
            levelToLoad = level["commandList"][rect.data].x;
        }
    }
}

但感谢您的帮助:)

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