javascript检查是否设置了数组键

Question

var place = []

place[0] = "Sant Marti de Canals";
place[1] = "Catalonia";
place[3] = "";
place[4] = "Spain";

placeTitle = place.join(",");

当前输出是"Sant Marti de Canals，Catalonia，，，西班牙“

怎么可能是“西班牙加泰罗尼亚的圣马蒂运河”？

Answer 1

为此编写您自己的代码可能会有所帮助

var place = []

place[0] = "Sant Marti de Canals"; place[1] = "Catalonia"; place[3] = ""; place[4] = "Spain";

var placeTitle ='';
for(var test in place) {
    placeTitle += place[test]!=''?place[test]+',':'';
}
placeTitle = placeTitle.substr(0,placeTitle.length-1)

Answer 2

您还可以定义过滤器函数，这在许多其他情况下都很有用。

Array.prototype.filter = function(p) {
    var a = [];
    p = p || function (x) {return x;}
    for (var i = 0; i<this.length; ++i) {
        if (p(this[i])) {
            a.push(this[i]);
        }
    }
    return a;
}

...

placeTitle = place.filter().join(', ');

Answer 3

placeCopy=[];
for(var i=0;i<place.length;i++){
  if(typeof place[i] != 'undefined' && place[i].length > 0){  
    placeCopy.push(place[i]);
  }
}
placeTitle = placeCopy.join(",");