javascript - 仅当在函数内部时，循环才会返回额外的时间

Question

对此非常陌生，如果我错过了一些非常简单的东西，那么抱歉。

我一直在尝试编写一些内容，它将返回对象的属性编号、属性名称和所有属性值的列表，格式为:

"n property - property value"

我确信我已经以一种完全过于复杂的方式解决了这个问题，但这是代码:

var person = {
    names: ["A", "B", "C"],
    dob: "D",
    age: 21,
    job: "E",
    car: ["F", 2, "G", "H", "I", "J", "K"],
    phone: "L",
    instrument: "M",
    parents: ["N", "O", "P"], 
    born: "Q",
    lives: "R",
    university: "S",
};

function lister (name) {
  for (i=0; i<(Object.keys(name).length); i++) {
  if (((Object.values(name)[i].constructor) == Array) === true) {
    for (x=0; x<(Object.keys(Object.values(name)[i]).length); x++) {
      console.log(i + " " + Object.keys(name)[i] + " - " + Object.values(Object.values(name)[i])[x]);
    }
  }else{
    console.log(i + " " + Object.keys(name)[i] + " - " + Object.values(name)[i]);
  }
}
};

console.log(lister(person));

for (i=0; i<(Object.keys(person).length); i++) {
  if (((Object.values(person)[i].constructor) == Array) === true) {
    for (x=0; x<(Object.keys(Object.values(person)[i]).length); x++) {
      console.log(i + " " + Object.keys(person)[i] + " - " + Object.values(Object.values(person)[i])[x]);
    }
  }else{
    console.log(i + " " + Object.keys(person)[i] + " - " + Object.values(person)[i]);
  }
};

问题是，当我在函数列表器(名称)中调用for循环时，它似乎额外运行了一次，给了我:

"0 names - A"

"0 names - B"

"0 names - C"

"1 dob - D"

...

"9 lives - R"

"10 university - S"

undefined

但是，当将 for 循环从函数中取出时(正如我在底部所做的那样)，它会正常返回，而不返回额外的“未定义”。我做错了什么？

Answer 1

这个额外的部分不是来自循环，而是来自函数调用。如果函数没有显式返回任何内容，则返回未定义，在下面的代码片段中，函数 lister 返回 x，因此您将看到 x 而不是 undefined >

var person = {
  names: ["A", "B", "C"],
  dob: "D",
  age: 21,
  job: "E",
  car: ["F", 2, "G", "H", "I", "J", "K"],
  phone: "L",
  instrument: "M",
  parents: ["N", "O", "P"],
  born: "Q",
  lives: "R",
  university: "S",
};

function lister(name) {
  for (i = 0; i < (Object.keys(name).length); i++) {
    if (((Object.values(name)[i].constructor) == Array) === true) {
      for (x = 0; x < (Object.keys(Object.values(name)[i]).length); x++) {
        console.log(i + " " + Object.keys(name)[i] + " - " + Object.values(Object.values(name)[i])[x]);
      }
    } else {
      console.log(i + " " + Object.keys(name)[i] + " - " + Object.values(name)[i]);
    }
  }
  return 'x'
};

console.log(lister(person));

for (i = 0; i < (Object.keys(person).length); i++) {
  if (((Object.values(person)[i].constructor) == Array) === true) {
    for (x = 0; x < (Object.keys(Object.values(person)[i]).length); x++) {
      console.log(i + " " + Object.keys(person)[i] + " - " + Object.values(Object.values(person)[i])[x]);
    }
  } else {
    console.log(i + " " + Object.keys(person)[i] + " - " + Object.values(person)[i]);
  }
};