javascript - 计算嵌套对象中的键

Question

我正在尝试统计嵌套 JS 对象中的键。我能够进入第一个级别，但我对如何让它深入嵌套对象并返回计数有点困惑。

var properties = {
prop1: '',
prop2: '',
prop3: '',
prop4: {
    subProp1: '',
    subProp2: '',
    subProp3: {
        subSubprop1: ''
        }
    }
}

var getCount = function (data) {
var count = 0;
for (var k in data) {
    if (properties.hasOwnProperty(k)) {
        ++count;
    }
}
console.log( "this is the count for level 0: " + count //returns 4);
console.log( "this is the count for level 1: " + count //should return 3);
console.log( "this is the count for level 2: " + count //should return 1);
return count;
}
getCount(properties);

Answer 1

如果属性是一个对象，你可以进行递归:

 var properties = {
        prop1: '',
        prop2: '',
        prop3: '',
        prop4: {
            subProp1: '',
            subProp2: '',
            subProp3: {
                subSubprop1: ''
            }
        }
    },
    count = [];

// i suggest to use named function for recursion, because the name is used
// inside the function. otherwise it is not safe, if the name does not
// match the given name at assignment
function getCount(data, level) {
    level = level || 0;
    count[level] = count[level] || 0;
    for (var k in data) {
        data.hasOwnProperty(k) && count[level]++;
        typeof data[k] === 'object' && getCount(data[k], level + 1);
    }
}

getCount(properties);
document.write('<pre>' + JSON.stringify(count, 0, 4) + '</pre>');

奖励:一个以函数式风格内置计数的版本

var properties = {
        prop1: '',
        prop2: '',
        prop3: '',
        prop4: {
            subProp1: '',
            subProp2: '',
            subProp3: {
                subSubprop1: ''
            }
        }
    };

function f(o, l, r) {
    l = l || 0;            
    return Object.keys(o).reduce(function (r, k) {
        r[l] = (r[l] || 0) + 1;
        typeof o[k] === 'object' && f(o[k], l + 1, r);
        return r;
    }, r || []);
}

document.write('<pre>' + JSON.stringify(f(properties), 0, 4) + '</pre>');