Check Javascript object undefined

Question

update

I am trying to test to see whether a Javascript variable is undefined.

How to make an object that is missing a variable or undefined

before thank you if it is willing to help

this my code

var mydata = {
  p001: "Product 1",
  p002: "Product 2",
  p003: "Product 3"
}

function test(e) {
  if (mydata === undefined || mydata === null) {
    document.getElementById("demo").innerHTML = "<em>No data</em>";
  } else {
    document.getElementById("demo").innerHTML = mydata[e];
  }
}

var mydata = {
  p001: "Product 1",
  p002: "Product 2",
  p003: "Product 3"
}

function test(e) {
  if (mydata === undefined || mydata === null) {
    document.getElementById("demo").innerHTML = "<em>No data</em>";
  } else {
    document.getElementById("demo").innerHTML = mydata[e];
  }
}

#demo {
  padding: 10px;
  margin: 0;
  border: 1px solid #2f9fd2;
  border-radius: 4px;
  background: #daf3ff;
}

<p>
  <button onclick='test("p001");'>Product 1</button>
  <button onclick='test("p002");'>Product 2</button>
  <button onclick='test("p003");'>Product 3</button>
  <button onclick='test("p10000");'>Test undefined</button>
</p>
<div id="demo"></div>

sorry my English is not good

Thank you

Your code in the snippet works totally fine. What exactly are you trying to ask? — Praveen Kumar Purushothaman
– Praveen Kumar Purushothaman, Commented Jul 16, 2018 at 11:13

sjahan · Accepted Answer · 2018-07-16 11:15:34Z

1

I think this is what you are looking for.

Just check if there is no value for the key e in mydata.

By the way, there is no array here. Using the proper terms is important. You work with an object and you want to check if a property of it is defined or not.

var mydata = {
	p001:"Product 1",
	p002:"Product 2",
	p003:"Product 3"
}

function test(e) {
  if (!mydata[e]) {
    document.getElementById("demo").innerHTML = "<em>No data</em>";	
	} else {
    document.getElementById("demo").innerHTML = mydata[e];
	}
}

#demo {
    padding: 10px;
    margin: 0;
    border: 1px solid #2f9fd2;
    border-radius: 4px;
    background: #daf3ff;
}

<p>
  <button onclick='test("p001");'>Product 1</button>
  <button onclick='test("p002");'>Product 2</button>
  <button onclick='test("p003");'>Product 3</button>
  <button onclick='test("p10000");'>Test undefined</button>
</p>

<div id="demo"></div>

edited Jul 16, 2018 at 11:15

answered Jul 16, 2018 at 11:14

sjahan

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Comments

Nina Scholz · Accepted Answer · 2018-07-16 11:15:31Z

You could extend the check for undefined values.

if (mydata === undefined || mydata === null || mydata[e] === undefined) {
                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^

var mydata = {
	p001:"Product 1",
	p002:"Product 2",
	p003:"Product 3"
}

function test(e){
   if (mydata === undefined || mydata === null || mydata[e] === undefined) {
    	document.getElementById("demo").innerHTML = "<em>No data</em>";	
	} 
    else {
    	document.getElementById("demo").innerHTML = mydata[e];
	}
}

#demo {
    padding: 10px;
    margin: 0;
    border: 1px solid #2f9fd2;
    border-radius: 4px;
    background: #daf3ff;
}

<p>
  <button onclick='test("p001");'>Product 1</button>
  <button onclick='test("p002");'>Product 2</button>
  <button onclick='test("p003");'>Product 3</button>
  <button onclick='test("p10000");'>Test undefined</button>
</p>

<div id="demo"></div>

Zeeshan Adil · Accepted Answer · 2018-07-16 11:21:39Z

0

I believe there is no need of doing two check for the same thing like this:

if (mydata === undefined || mydata === null) {
        document.getElementById("demo").innerHTML = "<em>No data</em>"; 
    }

do this instead with a == operator cause basically null == undefined so this will eventually save you as === checks for an exact match but == will give you true for both null and undefined as it does the type coercion for you:

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

answered Jul 16, 2018 at 11:21

Zeeshan Adil

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