地理位置，使用for和javascript循环 [英] Geolocation, loop with for and javascript

问题描述

我正在为移动网站开发地理定位工具，到目前为止，我已经了解到了这一点：

I'm working on a Geolocation tool for a mobile website and so far i got this:

地理位置验证 href = http://dev.opera.com/articles/view/how-to-use-the-w3c-geolocation-api/ rel = nofollow noreferrer>此处：

The Geolocation verification from here:

if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(successFunction, errorFunction);
} else {
    console.log('Geolocation not enabled in your browser.');
}

Caspar的 toRad（）函数< a href = https://stackoverflow.com/questions/5260423/torad-javascript-function-throwing-error>此处：

The toRad() function from Caspar's answer here:

if (typeof(Number.prototype.toRad) === "undefined") {
    Number.prototype.toRad = function() {
        return this * Math.PI / 180;
    }
}

和 successFunction（）从第一个链接可移动类型脚本和其他一些修改：

and the successFunction() from the first link, Movable Type Scripts and some others modifications:

function successFunction(position) {

    var lat1 = position.coords.latitude;
    var lon1 = position.coords.longitude;

    function calcdist(nLoja,nLat,nLong) {
        this.loja = nLoja;
        this.lat = nLat;
        this.long = nLong;
    }

    aLocal = new Array(3)
    aLocal[0] = new calcdist("leblon",-22.982279,-43.217792);
    aLocal[1] = new calcdist("ipanema",-22.98376,-43.212138);
    aLocal[2] = new calcdist("barra",-22.999118,-43.357867);

    var i = 0;
    //for (var i = 0; i < 4; i++){

        lat2 = aLocal[i].lat;
        lon2 = aLocal[i].long;

        var R = 6371;
        var dLat = (lat2-lat1).toRad();
        var dLon = (lon2-lon1).toRad();
        var lat1 = lat1.toRad();
        var lat2 = lat2.toRad();

        var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
                Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
        var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
        var d = R * c;

        var thediv = document.getElementById('locationinfo');
            thediv.innerHTML = '<p>Distance user-' + aLocal[i].loja + ': ' + d + '</p>';

    //}
}

我的桌面和我的iPhone。问题出在我注释 i = 0; 行并取消注释 for（）语句之后（以及作为结束括号）。 Chrome的控制台向我返回错误：

This works just fine on my desktop and my iphone. The problem comes when i comment the i=0; line and uncomment the for() statement right after (as well as the closing bracket). Chrome's console returns me an error:

Uncaught TypeError: Cannot read property 'lat' of undefined

为此行：

lat2 = aLocal[i].lat;

循环的原因是我想做x次数学运算以检查哪家商店更近到用户（通过获得用户与每个商店之间的最小距离）。但是我似乎无法找出为什么不允许循环的原因。

The reason for the loop is that i want to do the math x times to check which shop is closer to the user (by getting the smallest distance between user and each shop). But i can't seem to find out why it won't allow the loop.

提前很多感谢。

推荐答案

aLocal 具有三个元素。您的循环从0到3，所以有4个元素。

aLocal has three elements. Your loop goes from 0 to 3 so that are 4 elements.

for (var $i = 0; $i < aLocal.length; $i++) {
    //...
}

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