时间戳

首页 > 解决方案 > 需要访问函数中定义的变量。嵌套循环是解决方案吗？

javascript - 需要访问函数中定义的变量。嵌套循环是解决方案吗？

问题描述

我有以下代码，需要访问变量“密度”并将其放在弹出窗口中。密度是在 mapCities 函数中定义的，但是我添加的标记和我正在创建的弹出窗口是在地图城市函数之外的 for 循环中创建的，导致 ReferenceError: density is not defined index.html:151:42 . 这是预期的错误。我只是不知道如何访问该密度变量。它应该与嵌套循环一起使用吗？

              function mapCities(units) {
                for (var i = 0; i < cities.length; i++) {
                    var cityName = cities[i];
                    var cityNumPeeps = cityPops[i];
                    var cityZone = cityAreas[i];
                    var cityXY = cityCoords[i];
                    var density = calcPopDensity(cityNumPeeps, cityZone, units); // call calcPopDensity passing population, cityZone and units as arguments

                    console.log(density);
                }
            };

            function calcPopDensity(cityNumPeeps, cityZone, units) {
                if (units == "miles") {
                    return cityNumPeeps / cityZone // calculate population density in miles and return it 


                } else if (units == "km") {
                    return cityNumPeeps / cityZone * 1.60934 // calculate population density in miles and return it 

                }

            };

            for (var i = 0; i < cities.length; i++) {
                var cityName = cities[i];
                var cityNumPeeps = cityPops[i];
                var cityZone = cityAreas[i];
                var cityXY = cityCoords[i];
                var popup = `<b>${cityName}</b><br>
                    <b>population</b>: ${density}<br>`
                L.marker(cityXY).addTo(map) // add marker to map based on cityCoords array and bind to popup
                    .bindPopup(popup);
                console.log(popup)
                //if statement determines units to place in popup text
                if (units == "miles") {
                    popup += `miles`; // add text if if var density returns miles
                } else if (units == "km")
                    popup += `kilometers`; // add text if if var density returns kilometers
                L.marker(cityXY).addTo(map) // add popup again based on if statement
                    .bindPopup(popup);
                console.log(popup)

            }
```

​

标签： javascriptfunctionfor-loopvar

解决方案

只需为您需要的 for 循环的局部密度创建一个变量。密度变量超出范围，above因此您将无法按原样使用它。 

for (var i = 0; i < cities.length; i++) {
    var cityName = cities[i];
    var cityNumPeeps = cityPops[i];
    var cityZone = cityAreas[i];
    var cityXY = cityCoords[i];

    var density = calcPopDensity(cityNumPeeps, cityZone, units);

    var popup = `<b>${cityName}</b><br>
        <b>population</b>: ${density}<br>`
    L.marker(cityXY).addTo(map) // add marker to map based on cityCoords array and bind to popup
        .bindPopup(popup);
    console.log(popup)
    //if statement determines units to place in popup text
    if (units == "miles") {
        popup += `miles`; // add text if if var density returns miles
    } else if (units == "km")
        popup += `kilometers`; // add text if if var density returns kilometers
    L.marker(cityXY).addTo(map) // add popup again based on if statement
        .bindPopup(popup);
    console.log(popup)
}

推荐阅读