javascript - Array.reduce 和递归

Question

我试图在 Array.reduce 调用中嵌套一个递归函数。

但以下仅对第三种情况无效

const i1 = {'local': [['a','b']]};
const i2 = {'local': [['c','d']], 'recursive': []};
const i3 = {'local': [['c','d']], 'recursive': [{'local': [['e','f']]}]};

function reduce(current, result = []) {

    if(current.hasOwnProperty('local'))
       result.push(...current.local);

    if(current.hasOwnProperty('recursive'))
       result = current.recursive.reduce(reduce, result);
    //'result =' should be optional, but yields a wrong answer anyway

    return result;    
}

console.log(reduce(i1));
console.log(reduce(i2));
console.log(reduce(i3));

所以我没有调用 reduce，而是尝试了以下循环

for(var i = 0; i < current.recursive.length; ++i)
    result = reduce(current.recursive[i], result);
 //'result = ' is optional for it is passed by reference

并且有效。作为 JavaScript 的新手，我肯定错过了这里的一个关键特性，所以你能解释一下吗？

第三个实例的输出应该是

[ [ 'c', 'd' ], [ 'e', 'f' ] ]

但是是

{ local: [ [ 'e', 'f' ] ] }

或

[ [ 'c', 'd' ] ]

当 result = 被移除时。

Answer 1

问题是参数的顺序，reduce 回调函数的第一个参数是累加器而不是当前值。试试这个:

const i1 = {'local': [['a','b']]};
const i2 = {'local': [['c','d']], 'recursive': []};
const i3 = {'local': [['c','d']], 'recursive': [{'local': [['e','f']]}]};

function reduce(result, current) {

    if(current.hasOwnProperty('local'))
       result.push(...current.local);

    if(current.hasOwnProperty('recursive'))
       result = current.recursive.reduce(reduce, result);
    //'result =' should be optional, but yields a wrong answer anyway

    return result;    
}

console.log(reduce([], i1));
console.log(reduce([], i2));
console.log(reduce([], i3));