为什么此值等于“未定义”？ （javascript）

Question

I have a function for finding on which tile the mouse is on:

function testTile(mouseX, mouseY){
    if(mouseX<mapArray[0].length*20 && mouseY<mapArray.length*20){
        var tile = getTilePosition(mouseX-10, mouseY-10);
        selectedtile.x = tile.xtile, 
        selectedtile.y = tile.ytile;
    }
}

and a function for getting the tile position given x and y

function getTilePosition(x, y){
    var xtile = Math.floor(x/20);
    var ytile = Math.floor(y/20);
return{
    xtile : xtile,
    ytile : ytile
    }
}

but when I call selectedtile.x or selectedtile.y I get a value of 'undefined'. What's wrong?

Answer 1

It appears your values are declared inside the function and are out of scope.

Do this:

var selectedtile = new Object() //de OUTSIDE All functions.
//de this works too: var selectedtile = {}

function testTile(mouseX, mouseY){
    if(mouseX<mapArray[0].length*20 && mouseY<mapArray.length*20){
        var tile = getTilePosition(mouseX-10, mouseY-10);
        selectedtile.x = tile.xtile, 
        selectedtile.y = tile.ytile;
    }
}

function getTilePosition(x, y){
    var xtile = Math.floor(x/20);
    var ytile = Math.floor(y/20);
    return {
        xtile : xtile,
        ytile : ytile
    }
}