How to assert an `if` condition as truthy when an array is composed of undefined objects in Angular js

Question

I have an array named as joinedArray. In one case, it has the value [undefined, undefined].

I have written one if condition like:

if(joinArray === undefined){
    vm.selectedFriends = [];
    angular.forEach($scope.contacts, function(contact){
        if (contact.selected)
        vm.selectedFriends.push(contact.email);
    });

    $http({
        url: 'http://192.168.2.8:7200/api/creatList',
        method: 'POST',
        data: {wData:userData, uId:vm.uid, userName:vm.uName, email:vm.selectedFriends}
    }).success(function(res) {
        console.log("success");
    }, function(error) {
        console.log(error);
        alert('here');
    });
    $mdDialog.hide(userData);
} else {
    $http({
        url: 'http://192.168.2.8:7200/api/sendMail',
        method: 'POST',
        data: {wData:userData, email:joinArray, uId:vm.uid, userName:vm.uName}
    }).success(function(res) {
        console.log("success");
    }, function(error) {
        console.log(error);
        alert('here');
    });
    $mdDialog.hide(userData);
}

Sometimes joinedArray returns like [value, undefined] or [undefined, value]. But only when both values are undefined should it pass to the if condition, otherwise it should go to else condition.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every — Bergi, Sep 23 '16 at 08:06
Possible duplicate of [Check if array is empty or exists](http://stackoverflow.com/questions/11743392/check-if-array-is-empty-or-exists) — Peter Morris, Sep 23 '16 at 14:02

score 1 · Answer 1 · edited May 23 '17 at 12:00

1

Use Array.every...

var allAreUndefined = joinedArray.every(function(value) {
  return value === undefined;
});

To check if the array is defined you need to use typeof, as suggested in the answer to this question.

edited May 23 '17 at 12:00

Community

1
1

answered Sep 23 '16 at 08:04

Peter Morris

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I have edited my question how to use for that if condition. – Kevin Sep 23 '16 at 08:09
I have used this before that if condition and I made if condition like if(joinArray === allAreUndefined) but its not working it is going to else condition. – Kevin Sep 23 '16 at 09:25

score 0 · Answer 2 · edited May 23 '17 at 12:33

Use a stringified array, a regular expression replacement, and an empty string comparison. For example:

    /* If a stringified array consists of null values, convert it to an empty string, and return null
    */
    if (JSON.stringify(Array(10)).replace(/^\[(null[,\]])+/,"") === "")
      {
      console.log(null);
      }
    else
      {
      console.log(NaN);
      }

Or more specifically:

"use strict";

/* evaluate a stringified array to get the evaled values */
var foo = Function("return eval(JSON.stringify(Array(10)).replace(/null/g, undefined))")();


if (JSON.stringify(foo).replace(/^\[(null[,\]])+/,"") === "")
    {
    console.log("null");
    }
else
    {
    console.log("not null");
    }


/* 
Use foo.indexOf(null) before all this to avoid false positives
*/

References

How to assert an `if` condition as truthy when an array is composed of undefined objects in Angular js

2 Answers2