我对 HTML 没有经验，不知道为什么这个功能不起作用

Question

所以我目前正在使用谷歌地图 html api，我正在尝试添加这部分代码，当我这样做时，地图完全停止工作。我对 HTML 没有经验，但如果您知道语法错误或其他导致此功能无法正常工作的错误，请告诉我可能出了什么问题。

function calc_gallons() {
        var averagempg = parseInt(document.getElementById("averagempg").value):
        var gallons = 0;
        var total = 0;
        var myroute = result.routes[0];
        for (var i = 0; i < myroute.legs.length; i++) {
          total += myroute.legs[i].distance.value;
        }
        total = (total / 1000)*0.621371;
        document.getElementById('total').innerHTML = total;
        if averagempg > 0 {
            gallons = total / averagempg
            alert('This trip requires' + gallons + 'gallon(s). Have safe travels!')
        }
        else {
            alert('Your average MPG must be a positive number in order to calculate the gallons required for this trip.')
        }
      }

Answer 1

您的if 语句在其条件周围缺少括号。这段代码有效吗？

function calc_gallons() {
        var averagempg = parseInt(document.getElementById("averagempg").value):
        var gallons = 0;
        var total = 0;
        var myroute = result.routes[0];
        for (var i = 0; i < myroute.legs.length; i++) {
          total += myroute.legs[i].distance.value;
        }
        total = (total / 1000)*0.621371;
        document.getElementById('total').innerHTML = total;
        if (averagempg > 0) {
            gallons = total / averagempg
            alert('This trip requires' + gallons + 'gallon(s). Have safe travels!')
        }
        else {
            alert('Your average MPG must be a positive number in order to calculate the gallons required for this trip.')
        }
      }