如何确保javascript检查所有属性

Question

您好，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");

问题在于，它仅返回循环中的第一个结果，因此在这种情况下，它将仅检查是否在contacts [0] firstName === firstName中，然后即使contacts [1] firstName === firstName返回false

Answer 1

尝试这个：

    // 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，您可以只检查if if(obj[prop]) 。 我喜欢减少这种事情：

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