Understand “==” and “===” operator in JavaScript

Sourav.Kayal
Posted by in JavaScript category on for Beginner level | Points: 250 | Views : 5146 red flag

Understand “==” and “===” operator in JavaScript

Understand “==” and “===” operator in JavaScript

In this small article we will understand the difference between “==” and “===” operator in JavaScript. It’s very important to understand the difference between them otherwise programmer might do big mistake in code development and as side effect program might work unexpectedly.

Let’s try to understand the basic difference between them.

“==” operator checks the value not type where “===” operator check value and type both. Let’s try to implement with suitable example.

Understand “==” operator

In this section we will understand “==” operator with example. In first example we will compare Boolean value with string. Have a look on below code.

<body>
    <form id="form1" runat="server">
        <script>
            var value = false;
            if (value == 0)
                alert("Both are same, but type is not")
            else
                alert("Not Same");
 
        </script>
    </form>
</body>

In this example within if condition we are checking “false” with “0”. And the output screen is saying that.


Both are same in terms of value. Try with string and “false”, let’s see the result.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="JavaScript.aspx.cs" Inherits="JavaScript.JavaScript" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
</head>
<body>
    <form id="form1" runat="server">
        <script>
            var value = false;
            if (value == "0")
                alert("false and 0 are same")
            else
                alert("Not Same");
 
        </script>
    </form>
</body>
</html>

Here is sample output. Again we are seeing that both are same.


So, we are seeing that “==” operator is checking only value not type. Now we will see how “===” operator works.

Understand “===” operator

As we told earlier that “===” checks the value and it’s type. Let’s try to compare “false” and “0” using “===” operator. Here is sample code.

<body>
    <form id="form1" runat="server">
        <script>
            var value = false;
            if (value === "0")
                alert("false and 0 are same")
            else
                alert("false and  0 ,type mismatch");
 
        </script>
    </form>
</body>

Here is sample output. We are seeing that the type does not match.


Let’s try with both Boolean variables. Have a look on below code.

<body>
    <form id="form1" runat="server">
        <script>
            var value = false;
            if (value === false)
                alert("false and false matches")
            else
                alert("type mismatch");
 
        </script>
    </form>
</body>

This is the output.


We are seeing that both are same in terms of value and type because if condition has satisfied.

Conclusion:-

In this small article we have seen how “==” and “===” operator works in JavaScript.

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About the Author

Sourav.Kayal
Full Name: Sourav Kayal
Member Level: Silver
Member Status: Member,MVP
Member Since: 6/20/2013 2:09:01 AM
Country: India
Read my blog here http://ctrlcvprogrammer.blogspot.in/
http://www.dotnetfunda.com
I am .NET developer working for HelixDNA Technologies,Bangalore in healthcare domain. Like to learn new technology and programming language. Currently working in ASP.NET ,C# and other microsoft technologies.

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