scope in javascript.. parent scope variable not retaining value

Question

I am a newbie to javascript..have gone thru multiple scope related blogs and several answers on stackoverflow..but not sure why this code doesnt work..

 function checkPhoneEmail(element, index, array) {
    var _contact = {};
    var _phone_empty = true;
    var _email_empty = true;
    var _phones_to_store = [];
    var _emails_to_store = [];
    var _prev_phone_number;
    var _phone;
    var i;
    //function to check if this phone 
    // should be included
    function checkMobilePhone(ph_element) {
        var _match;


        _match = ph_element.type.match(/mobile/i);
        if (_match && ph_element.value.length >= 10 && !(ph_element.value.match(/^800/) || ph_element.value.match(/^1800/) || ph_element.value.match(/^1-800/))) {
            return true;
        };
        return false;
    };

    if (!_.isEmpty(element.phoneNumbers)) {

        for (i = 0; i < element.phoneNumbers.length; i++) {
            console.log('prev num: ' + _prev_phone_number);
            console.log('curr num: ' + element.phoneNumbers[i].value)
            if (!_.isEqual(_prev_phone_number, element.phoneNumbers[i].value)) {
                if (checkMobilePhone(element.phoneNumbers[i])) {
                    _phone = {
                        id: element.phoneNumbers[i].id,
                        value: element.phoneNumbers[i].value
                    };
                    _phones_to_store.push(_phone);
                    console.log('phone to store: ' + element.phoneNumbers[i].value)
                };
            };
            _prev_phone_number = element.phoneNumbers[i].value;
            console.log('prev1 num: ' + _prev_phone_number);
        };

        _phone_empty = false;
    };

    if (!_.isEmpty(element.emails)) {

    };

};

why is the _prev_phone_number not being set ? I see it at prev1 num..but when you look for the next element its set back to undefined...my understanding is for doesnt create a new scope ? is this incorrect ?

I am trying to remove duplicates from phone contacts array (from cordova contacts) and doing some very basic checks to eliminate all numbers except a valid us mobile # for a mobile app..using above logic if a contact has multiple entries in contacts for same phone number i am seeing duplicates..Tried above logic with foreach and also _.uniq ... but same result..

Any help is appreciated.

sample Data:

{
    "id" : "1916",
    "rawId" : "1911",
    "displayName" : "John Doe",
    "name" : {
        "familyName" : "Doe",
        "formatted" : "John Doe",
        "givenName" : "John"
    },
    "nickname" : null,
    "phoneNumbers" : [{
            "type" : "mobile",
            "value" : "+1 999 666 9175",
            "id" : "11994",
            "pref" : false
        }, {
            "type" : "mobile",
            "value" : "+1 999 666 9175",
            "id" : "12001",
            "pref" : false
        }
    ],
    "emails" : null,
    "addresses" : null,
    "ims" : null,
    "organizations" : null,
    "birthday" : null,
    "note" : "",
    "photos" : null,
    "categories" : null,
    "urls" : null
}

Answer 1

A for loop does not create its own scope. The issue is that you are trying to log to the console an undefined value.

for (i = 0; i < element.phoneNumbers.length; i++) {
        //_prev_phone_number is undefined here.
        console.log('prev num: ' + _prev_phone_number); 
        console.log('curr num: ' + element.phoneNumbers[i].value)
        if (!_.isEqual(_prev_phone_number, element.phoneNumbers[i].value)) {
            if (checkMobilePhone(element.phoneNumbers[i])) {
                _phone = {
                    id: element.phoneNumbers[i].id,
                    value: element.phoneNumbers[i].value
                };
                _phones_to_store.push(_phone);
                console.log('phone to store: ' + element.phoneNumbers[i].value)
            };
        };
        //This is the first time you have defined _prev_phone_number
        _prev_phone_number = element.phoneNumbers[i].value;
        console.log('prev1 num: ' + _prev_phone_number);
    };

You should probably check to see if _prev_phone_number has been defined before logging it to the console.

if(_prev_phone_number){
  console.log('prev num: ' + _prev_phone_number);
}

This would ensure that you are not logging an undefined value.

Answer 2

Instead of using the variable _prev_phone_number , why don't you just access element.phoneNumbers[i-1].value ? No need to introduce a new variable for it.

If that doesn't work, then something is clobbering your object and we will need to look deeper.