If else数组查找

你正在做的一个错误是hasOwnProperty返回一个布尔值，但你正在将它与字符串中传递的值进行比较。此外，如果您从每个if/else块返回，则确实不需要else/if，您可以只使用if:

你可以这样考虑你的情况:

// store current contact in a variable
var contact = contacts[i];
// get properties from the current contact
var name = contact.firstName;
var propValue = contact[prop];
// check for existence of the passed in first name and property
var hasName = name === firstName;
var hasProp = contact.hasOwnProperty(prop);
// if it has both, return property
if (hasName && hasProp) {
  return propValue;
}
// if it only has the name, return 'no such prop'
if (hasName) {
  return 'no such prop';
}
// otherwise it has neither so we return 'no such contact'
return 'no such contact';

var contacts = [{
  "firstName": "Akira",
  "likes": "beer",
}];
function lookUpProfile(firstName, prop) {
  for (var i = 0; i < contacts.length; i++) {
    // store current contact in a variable
    var contact = contacts[i];
    // get properties from the current contact
    var name = contact.firstName;
    var propValue = contact[prop];
    // check for existence of the passed in first name and property
    var hasName = name === firstName;
    var hasProp = contact.hasOwnProperty(prop);
    // if it has both, return property
    if (hasName && hasProp) {
      return propValue;
    }
    // if it only has the name, return 'no such prop'
    if (hasName) {
      return 'no such prop';
    }
    // otherwise it has neither so we return 'no such contact'
    return 'no such contact';
  }
}
console.log(lookUpProfile("Akira", "likes")); // beer
console.log(lookUpProfile("Akira", "something else")); // no such prop
console.log(lookUpProfile("Someone else", "likes")); // no such contact

或者，代替循环，您可以使用Array.prototype.find按名字查找人员，然后根据find()的结果返回:

// finds the person with the provided name or return undefined
var contact = contacts.find(function(c) {
  return c.firstName === firstName;
});
// if no contact exists, return 'no such contact'
if (!contact) {
  return 'no such contact';
}
// if contact doesn't have the prop, return 'no such prop'
if (!contact.hasOwnProperty(prop)) {
  return 'no such prop';
}
// otherwise return the prop value
return contact[prop];

var contacts = [{
  "firstName": "Akira",
  "likes": "beer",
}];
function lookUpProfile(firstName, prop) {
  // finds the person with the provided name or return undefined
  var contact = contacts.find(function(c) {
    return c.firstName === firstName;
  });
  // if no contact exists, return 'no such contact'
  if (!contact) {
    return 'no such contact';
  }
  // if contact doesn't have the prop, return 'no such prop'
  if (!contact.hasOwnProperty(prop)) {
    return 'no such prop';
  }
  // otherwise return the prop value
  return contact[prop];
}
console.log(lookUpProfile("Akira", "likes")); // beer
console.log(lookUpProfile("Akira", "something else")); // no such prop
console.log(lookUpProfile("Someone else", "likes")); // no such contact

我想你从nem035的帖子中得到了答案。

如果您想探索另一种方法，您仍然可以看到此片段。

你可以使用filter属性来首先过滤与名字匹配的json对象。然后检索通过prop传递的键的值。

var contacts = [
    {
        "firstName": "Akira",
        "likes": "beer",
    }]
function lookUpProfile(firstName, prop){
var _toReturn =""
//_inArray will only have matched json object
var _inArray=contacts.filter(function(item){ 
  return item.firstName = firstName;
})
if(_inArray.length !==0){
console.log(_inArray[0])
  _toReturn =_inArray[0][''+prop+''];
}
// here you can also check if key prop exist in current object
else if(_inArray.length ==0) { 
_toReturn="no such contact";
}
return _toReturn;
}
document.write('<pre>'+lookUpProfile("Akira","likes")+'</pre>')

JSFIDDLE

您的代码永远不会执行整个for循环。在循环的第一个元素上，所有选项都返回一个值。

你的函数正在尝试做太多事情。如果将功能分成更小的函数，工作起来会更好，也更容易。

我将首先拆分查找联系人的功能:

function findContact(firstName) {
    for (var i = 0; i < contacts.length; i++) {
        var name = contacts[i].firstName;
        if(name === firstName) {
            return contacts[i];
        }
    }
    // contact was not found.
    return undefined;
}

function lookUpProfile(firstName, prop) {
    var contact = findContact(firstName);
    // undefined is a falsy value
    if(!contact) {
       return "no such contact";
    }
    // no need to else because the if branch terminates the function with a return
    var propz = contact.hasOwnProperty(prop);
    if(!propz) {
        return "no such property";
    }
    // again, no need to add an else
    return contact[prop];
}
lookUpProfile("Akira", "lastName");

然后，您可以使用Array.find将findContact函数代码替换为函数实现，如:

function findContact(firstName) {
    return contacts.find(function(contact) {
       return contact.firstName === firstName;
    }
}

或者如果你的代码将在ES6上运行，你可以再简化一点:

function findContact(firstName) {
    return contacts.find(contact => contact.firstName === firstName);
}

我更喜欢使用for in循环数组对象。你也应该在循环之外返回你的结果。你可以通过Object.keys()获得对象键。

var contacts = [{
  "firstName": "Akira",
  "likes": "beer",
},
{
    "firstName":"Suu",
    "likes" : "computer"
}];
function lookUpProfile(firstName, prop) {
  for (var i in contacts) {
    var name = contacts[i].firstName;
    var propz = Object.keys(contacts[i])[1];    
    if (name == firstName && propz == prop) {
      result = contacts[i][prop];
    } else if (prop != propz && firstName == name) {
       result = "no such property";
    } else if (firstName !== name && prop == propz) {
       result = "no such contact";
    }
  }
  return result;
}
console.log(lookUpProfile("Suu","likes"));