Question

嗨我正在尝试检查联系人是否存在以及是否具有特定属性然后将其返回

var 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 lookUp(firstName, prop) {
    var i;
    for (i = 0; i < contacts.length; i++) {
        if (contacts[i].firstName === firstName && contacts[i].hasOwnProperty(prop)) {
            return contacts[i][prop];
        } else if (contacts[i].firstName !== firstName) {
            return "No such contact";
        } else if (contacts[i].firstName === firstName && contacts[i].hasOwnProperty(prop) === false) {
            return "No such property";
        }
    }
}

lookUp("Harry", "likes");

问题是它只返回循环中的第一个结果，所以在这种情况下它只会检查联系人[0] firstName === firstName中是否然后返回false，即使联系人[1] firstName === firstName

Answer 1

试试这个：

    // Returns:
    //    contact prop if: contact with prop found
    //    true if: contact found, but not prop
    //    false if: not contact found
    function lookUp(firstName, prop) {
        var i, nameFound = false;
        // Starts a loop that looks every contact until the list ends or until firstName with prop is found
        for (i = 0; i < contacts.length; i++) {
            if (contacts[i].firstName === firstName ) {
                // If found, the function return the property "prop" of the contact named "firstName"
                // Note that if there is 2 persons with the same name and both has prop, it returns the first one on the list
                if(contacts[i].hasOwnProperty(prop)){
                    return contacts[i][prop];
                }
                else{
                    nameFound = true;
                }   
            }

        }
        // If the script reach this place, it's because the person wasn't found or was found but hasn't the prop
        return nameFound;
    }

Answer 2

function lookUp(firstName, prop) {
    var i;
    for (i = 0; i < contacts.length; i++) {
        if (contacts[i].firstName === firstName) {
           if(contacts[i].hasOwnProperty(prop)){
              return contacts[i][prop];
            }else{
              return "No such property";
            }
        }
    }
    return "No such Contact";
}

Answer 3

要检查对象是否具有属性，您只需要if(obj[prop])。我喜欢reduce这类事情：

function lookUp (firstName, prop) {
    return contacts.reduce(
        function (found, contact) {
            if (contact[prop] && contact.firstName === firstName)
                found.push(contact);
            return found;
        }, []
    );
}

如何确保javascript检查所有属性

3 个答案: