需要访问函数中定义的变量。嵌套循环是解决方案吗？

Question

我有以下代码，需要访问变量 "density" 并将其放在弹出窗口中。密度在 mapCities 函数中定义，但我添加的标记和我创建的弹出窗口是在 map cities 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。应该使用嵌套循环吗？

              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)

            }
```

Answer 1

只需在需要的地方为 for 循环的局部密度创建一个变量。 above 密度变量超出范围，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)
}

需要访问函数中定义的变量。嵌套循环是解决方案吗？

Need to access variable defined in a function. Is nested loop the solution?

javascript

for-loop

var

function