javascript - 递归函数无法正常工作

Question

我有一个递归函数，它应该循环遍历 json 对象并输出表达式。但是，我的回避似乎已关闭，因为它在输出 field1 != '' AND field3 == '' 时应该输出 field1 != '' AND field2 == '' AND field3 == ''

我已经尝试了几个不同的东西，唯一能让它工作的方法是创建一个全局变量 outstring 而不是将它传递给函数。我在哪里？当我单步执行它时，我看到了一个正确的结果，但是一旦堆栈反转，它就会开始重置 outstring，然后再次将其堆叠起来，但会遗漏中间部分 (field2)。

JSFiddle

function buildString(json, outstring) {
        var andor = json.condition;
    for (var rule in json.rules) {
        if (json.rules[rule].hasOwnProperty("condition")) {
            buildString(json.rules[rule], outstring);
        } else {
            var field = json.rules[rule].id;
            var operator = json.rules[rule].operator;
            var value = json.rules[rule].value == null ? '' : json.rules[rule].value;
            outstring += field + ' ' + operator + ' ' + value;
            if (rule < json.rules.length - 1) {
                outstring += ' ' + andor + ' ';
            }
        }
    }
    return outstring;
}

var jsonObj = {"condition":"AND","rules":[{"id":"field1","operator":"!= ''","value":null},{"condition":"AND","rules":[{"id":"field2","operator":"== ''","value":null}]},{"id":"field3","operator":"== ''","value":null}]};

$('#mydiv').text(buildString(jsonObj, ""));

Answer 1

该函数返回一个字符串。

当您从函数自身内部递归调用函数时，您不会对该实例返回的字符串做任何事情，只是调用无处可返回的函数

改变:

    if (json.rules[rule].hasOwnProperty("condition")) {
       buildString(json.rules[rule], outstring);
    } 

到

    if (json.rules[rule].hasOwnProperty("condition")) {
       // include the returned value in concatenated string
       outstring += buildString(json.rules[rule], outstring);
    }

DEMO