javascript - 类型错误 : Cannot read property '0' of undefined when comparing the arrays?

Question

我有一个包含 JSON 值的数组

category = [ {"categoryName":"abcd","productName":"chicken biriyani","price":100,"quantity":"medium"}, {"categoryName":"biriyani","productName":"mutton biriyani","price":130,"quantity":"medium"} ]

我必须检查上述类别数组所需的参数。 所以我创建了一个必需的参数数组。 var reqarray = ['类别名称','产品名称','价格','数量'];

我创建了示例代码来检查 reqarray 的值和类别的每个值。但它不起作用

var categoryList = [ {"categoryName":"abcd","productName":"chicken biriyani","price":100,"quantity":"medium"}, {"categoryName":"biriyani","productName":"mutton biriyani","price":130,"quantity":"medium"} ];
for(var i in categoryList){

        var reqarray =['categoryName','productName','price','quantity'];
        for(var j in arr){
            if(categoryList[i].reqarray[j]=='null' || categoryList[i].reqarray[j] == " "){
                console.log("data is null");
            }
            else if(categoryList[i].reqarray[j] == undefined){
                console.log("required parameters");
            }
            else{
                console.log("ok");
            }
        }
    }
}

此代码显示错误:

TypeError: Cannot read property '0' of undefined

Answer 1

可以将对象视为关联数组(也称为映射、字典、哈希、查找表)。该数组中的键是对象属性的名称。

访问属性有两种方法:点表示法和方括号表示法。

点符号:

get = object.property;
object.property = set;

使用点表示法调用方法:

document.createElement('pre');

括号符号

get = object[property_name];
object[property_name] = set;

使用方括号表示法调用:

document['createElement']('pre');

在这种情况下，文字'createElement'是已知的，您可以使用点运算符直接访问该属性。如果 createElement 是表达式求值的结果，那么您需要使用方括号表示法，从而指示 JS 编译器首先求方括号内的内容，然后访问 处的值评估对象的属性。

var categoryList = [ {"categoryName":"abcd","productName":"chicken biriyani","price":100,"quantity":"medium"}, {"categoryName":"biriyani","productName":"mutton biriyani","price":130,"quantity":"medium"} ];
for(var i in categoryList){

        var reqarray =['categoryName','productName','price','quantity'];
        for(var j in reqarray){
            if(categoryList[i][reqarray[j]]=='null' || categoryList[i][reqarray[j]] == " "){
                console.log("data is null");
            }
            else if(categoryList[i][reqarray[j]] == undefined){
                console.log("required parameters");
            }
            else{
                console.log("ok");
            }
        }
    }