以编程方式在javascript中选择对象的属性

Question

当我使用date_narrow(pdb, "datepub", "1980", "2000")调用此函数时，我期望返回的计数为2，并且选择将pdb [0]。设置为false。相反，我的调试器显示arr [k] .dfield总是未定义的，而我希望它是pdb [k] .datepub。也就是说，我试图在运行时选择对象arr [k]的属性。有关如何正确执行此操作的任何建议？

var date_narrow = function (arr, dfield, earlier_date, later_date) { 
    var count = 0; 
    for (var k = 0; k < arr.length; k++) { 
     if (arr[k].selected) { 
      // following are string comparisons 
      if ((arr[k].dfield < earlier_date) || (arr[k].dfield > later_date)) { 
       arr[k].selected = false; 
      } else { 
       count = count + 1; 
      } 
     } 
    } 
    return (count); 
}; 

pdb = [{ 
    datepub: "2012", 
    selected: true 
}, { 
    datepub: "1999", 
    selected: true 
}, { 
    datepub: "1980", 
    selected: true 
}]; 

Answer 1

在JavaScript中，数组语法（obj[...]）也适用于通过名字来访问一个对象的属性：

var date_narrow = function (arr, dfield, earlier_date, later_date) { 
    var count = 0; 
    for (var k = 0; k < arr.length; k++) { 
     if (arr[k].selected) { 
      // following are string comparisons 
      if ((arr[k][dfield] < earlier_date) || (arr[k][dfield] > later_date)) { 
       arr[k].selected = false; 
      } else { 
       count = count + 1; 
      } 
     } 
    } 
    return (count); 
}; 

Demonstration