为什么我的函数在更新 if 语句后无法识别数组中的值？

Question

我试图获得联系人的数据时，名称实际上存在于我的数组，当它不"没有这样的联系人"提示符，就像这样，它工作了，我得到"Vos">

const contacts = [
{
firstName: "Akira",
lastName: "Laine",
number: "0543236543",
likes: ["Pizza", "Coding", "Brownie Points"],
},
{
firstName: "Harry",
lastName: "Potter",
number: "0994372684",
likes: ["Hogwarts", "Magic", "Hagrid"],
},
{
firstName: "Sherlock",
lastName: "Holmes",
number: "0487345643",
likes: ["Intriguing Cases", "Violin"],
},
{
firstName: "Kristian",
lastName: "Vos",
number: "unknown",
likes: ["JavaScript", "Gaming", "Foxes"],
},
];
function lookUpProfile(name, prop) {
for (var i = 0; i < contacts.length; i++) {

if (contacts[i].firstName === name) {
if (contacts[i].hasOwnProperty(prop)) {
return contacts[i][prop];
} else {
return "No such property"
}
}
} 
}
lookUpProfile("Kristian", "lastName");

但是当我添加了额外的东西，如果它不再识别这个名字，我就会得到&;No such contact&;我想是一些非常简单和明显的东西，但我就是不明白为什么

const contacts = [
{
firstName: "Akira",
lastName: "Laine",
number: "0543236543",
likes: ["Pizza", "Coding", "Brownie Points"],
},
{
firstName: "Harry",
lastName: "Potter",
number: "0994372684",
likes: ["Hogwarts", "Magic", "Hagrid"],
},
{
firstName: "Sherlock",
lastName: "Holmes",
number: "0487345643",
likes: ["Intriguing Cases", "Violin"],
},
{
firstName: "Kristian",
lastName: "Vos",
number: "unknown",
likes: ["JavaScript", "Gaming", "Foxes"],
},
];
function lookUpProfile(name, prop) {
for (var i = 0; i < contacts.length; i++) {

if (contacts[i].firstName === name) {
if (contacts[i].hasOwnProperty(prop)) {
return contacts[i][prop];
} else {
return "No such property"
}
} else if (contacts[i].firstName[name] === undefined) {
return "No such contact"
}
} 
}
lookUpProfile("Kristian", "lastName");

Answer 1

问题是您在第二个代码片段中的第一次迭代之后从循环返回。因此，您只检查第一个项目，然后返回"No such contact"。看起来你只有在没有找到联系人的情况下才想在最后回来。我添加了一个控制台日志，显示循环经过了多少次迭代，这应该有助于故障排除。

const contacts = [
{
firstName: "Akira",
lastName: "Laine",
number: "0543236543",
likes: ["Pizza", "Coding", "Brownie Points"],
},
{
firstName: "Harry",
lastName: "Potter",
number: "0994372684",
likes: ["Hogwarts", "Magic", "Hagrid"],
},
{
firstName: "Sherlock",
lastName: "Holmes",
number: "0487345643",
likes: ["Intriguing Cases", "Violin"],
},
{
firstName: "Kristian",
lastName: "Vos",
number: "unknown",
likes: ["JavaScript", "Gaming", "Foxes"],
},
];
function lookUpProfile(name, prop) {
for (var i = 0; i < contacts.length; i++) {
console.log('Loop: ' + i);
if (contacts[i].firstName === name) {
if (contacts[i].hasOwnProperty(prop)) {
return contacts[i][prop];
} else {
return "No such property"
}
} else if (contacts[i].firstName[name] === undefined) {
return "No such contact"
}
} 
}
console.log(lookUpProfile("Kristian", "lastName"));