Question

Working with Google Maps, I have the following code:

var tileNames = ["base", "parking", "access"];
var mapType = {};

for (var i = 0; i < tileNames.length; i++) {
    var tileOptions = {
    getTileUrl: function(coord, zoom) {
        return "/maps/tiles/tiles" + tileNames[i] + "/" + zoom + "_" + coord.x + "_" + coord.y + ".png";
    },
    tileSize: new google.maps.Size(256, 256)
    };
mapType[tileNames[i]] = new google.maps.ImageMapType(tileOptions);
};

Here is my issue: the “tileNames[i]” in the “getTileUrl” function is undefined when the function is executed. However, the “tileNames” array is only meant to be used here in defining the “mapType” object and thus, unlike the “coord” and “zoom” variables which are passed to the function, I’m looking to use “tileNames[i]” to define that part of the function. Thus, ideally, the function assigned to mapType.parking would look like this…

function(coord, zoom) {
    return "/maps/tiles/tilesparking/" + zoom + "_" + coord.x + "_" + coord.y + ".png";
};

…after the function is defined in the first piece of code. Is there any way to take the value of a variable/array and use it to statically define a function while maintaining the other two variables as variables.

---

Edit: Looking at the various answers below, the following is the best I’ve been able to achieve thus far. While bind might be the ideal approach in a more general scenario, in this specific case, “getTileUrl:” apparently wants a specific syntax and placing the bind around the function defined for it causes errors for Maps. In trying KGZM’s suggestion, it works in everything up to date and not in IE8 and below.

var tileNames = ["beloit", "parking", "access_p"];
var mapType = {};

for (var i = 0; i <= (tileNames.length - 1); i++) {
    (function(i) {
        tileOptions = {
            getTileUrl: function(coord, zoom) {
                return "/maps/tiles/tiles" + tileNames[i] + "/" + zoom + "_" + coord.x + "_" + coord.y + ".png";
            },
            tileSize: new google.maps.Size(256, 256)
        };
        mapType[tileNames[i]] = new google.maps.ImageMapType(tileOptions);
    })(i);
};

Answer 1

There is a functional programming concept that can handle this well

Basically, your function actually has three arguments, the zoom variable, the coord object, and the tileNames[i] value, but you want the tileNames[i] value to be fixed to a particular value at one time in your code, and leave the other two variables as actually variable.

function getTileUrlBuilder(tilename) {
    return function(coord, zoom) {
        return "/maps/tiles/tile" + tilename + "/" + zoom + "_" + coord.x + "_" + coord.y;
    };
}

Then you can use this function in your loop. However, since this is actually a common operation, you can use the bind method to handle this:

(function(tilename, coord, zoom) {
    return "/maps/tiles/tile" + tilename + "/" + zoom + "_" + coord.x + "_" + coord.y
}).bind(this, tileNames[i]);

That will “bind” the implicit this to the current this, and then bind the first argument to the current value of tileNames[i].

EDIT: This, I think, should be the working code.

var tileNames = ["beloit", "parking", "access_p"];
var mapType = {};

function getTileUrlFull(tileName, coord, zoom) {
    return "/maps2/tiles/tiles" + tileName + "/" + zoom + "_" + coord.x + "_" + coord.y + ".png"
}

for(var i = 0; i < tileNames.length; i++) {
    mapType[tileNames[i]] = new google.maps.ImageMapType({
        getTileUrl: getTileUrlFull.bind(this, tileNames[i]),
        tileSize: new google.maps.Size(256, 256)
    });
}