typeError is null when variable defined as null

Question

code have to do 3 things

get json output of user.
get user status on-line or off-line (if data.stream === null) user is off-line
create user with nickname and status.
push that user into array. lastData array

1st problem i get TypeError data.sream is null even if i define null as in examples. some people say`ed that i can just ignore that, but i want to ask professionals -- Pritam Banerjee answer this question thank you

2nd problem is that user is not pushed into array. only same user is pushed few times in array. Code is here Fiddle

sorry if question is not good but i dont know where else to ask.

var mynull = null;

if (typeof mynull === null) {  // have to be   if(mynull == null)
    // my code
} 
else
  //my code

// building prototype name & status
  function userStatus(name, status) {
    this.name = name;
    this.status = status;
  } // prototype

var showUserList = ["OgamingSC2", "habathcx", "RobotCaleb", "noobs2ninjas"]
var lastData = []; // where to push users
for (var i = 0; i < showUserList.length; i++) {
  
var user = showUserList[i]; // get username from array
var useris = showUserList[i] // --//--

useris = new userStatus(user, 'Chanel is Offline');
            lastData.push(useris);
  
  console.log(lastData[i].name + '' + lastData[i].status);
  }

Oriol · Accepted Answer · 2016-12-04 01:20:02Z

1

Some things you must know about the typeof operator:

It always returns a string. Never compare the returned value to a non-string using ===.
It's horribly broken because it doesn't always not return the Type of the value.
For example, typeof null returns the string 'object'.

The proper way to compare mynull with null is mynull === null.

You can also use mynull == null to detect if it's either null or undefined.

edited Dec 4, 2016 at 1:20

answered Dec 4, 2016 at 1:08

Oriol

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2 Comments

EdenLT Over a year ago

that mean i can write just if (typeof null === 'object') and it would be fine?

Oriol Over a year ago

typeof null === 'object' would always be true. To compare with null, use mynull === null

Scott Marcus · Accepted Answer · 2016-12-04 01:25:23Z

null is an important primitive type in JavaScript. It is essentially a special value that indicates that there is no value! Initializing your variables to null when you don't know yet what their actual value will be later on is a very good best-practice in JavaScript, because if you wind up getting an error (like the one you are getting now (TypeError data.sream is null), it tells you that you never actually supplied a useful value to the variable.

When it comes to testing for null, you have a few options, but something that is important to remember is that JavaScript is loosely typed and values can and do change their type simply based on the way you use them. null is what's known as a "falsey" value, that is, if you convert it to a Boolean, it converts to false. Other "Falsey" values include: 0, undefined, "" and false. Just about every non-empty, non-zero, non-undefined value is "truthy" and will convert to true if forced into a Boolean.

So, if you really just want to know if your variable is still null or does it have meaningful data, you can leverage this loose typing like the following because the value of myNull will be converted to a Boolean so that the if statement can be evaluated.

Ask yourself if you really care if your variable has the exact value of null or do you just need to know if your variable has data that you can use? An explicit test for null may not really even be needed.

var myNull = null;
var myNull2 = null;

// We're only going to give one of the variables a value
myNull2 = "something";

if(myNull){
 // myNull is NOT null
 console.log("myNull is NOT null and has a value of: " + myNull);    
} else {
 // myNull is null
 console.log("myNull IS null and has a value of: " + myNull);      
}

if(myNull2){
 // myNull2 is NOT null
 console.log("myNull2 is NOT null and has a value of: " + myNull2);    
} else {
 // myNul2l is null
 console.log("myNul2l IS null and has a value of: " + myNull2);      
}

Pritam Banerjee · Accepted Answer · 2016-12-04 01:32:24Z

0

This will not work as:

typeof null === 'object';

So it will always return an object and hence your code will not work.

Rather you can try:

if (myNull == null){
   // your code here.
}

Also can try as suggested by Scott, but the if else would be the other way round:

if (myNull){}

edited Dec 4, 2016 at 1:32

answered Dec 4, 2016 at 1:08

Pritam Banerjee

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10 Comments

Scott Marcus Over a year ago

A better answer would be: if (myNull){} because this approach doesn't account for undefined values.

Pritam Banerjee Over a year ago

@ScottMarcus Agreed. Added that to my answer as well.

EdenLT Over a year ago

but if i using if (myNull){} code goes to else {} and anyway Firefox in console shows TypeError data.stream is null

Pritam Banerjee Over a year ago

@EdenLT Yes, use my first one.

EdenLT Over a year ago

@ Pritam Banerjee can i ignore in console TypeError? i getting data.stream is null but function is working

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