Understanding the Membership Operator in Blogger Template Code - KodeRian

If you’ve been customizing your Blogger template and stumbled upon the mysterious membership operators like in and contains, you’re not alone. These operators often appear in Blogger’s XML logic, helping creators perform comparisons and conditional rendering. Simply put, they check whether a specific value exists inside an array—and then return a Boolean result (true or false).

In this guide, we’ll break down the Operator Membership in Blogger—what it does, how it works, and how you can use it to make your Blogger templates more dynamic and intelligent. We’ll also cover practical examples, advanced tricks, common mistakes, and even some troubleshooting advice.

What Is the Membership Operator in Blogger?

The membership operator is used to check if a value exists within a given array or list. It compares a single value—like a name, number, or boolean—with the elements inside an array and then returns a true or false response.

For example, if you want to check whether the name “budi” exists inside an array like ["budi", "ani", "kaka budi"], the operation will return true. If it’s not found, it returns false.

This operator is highly useful in Blogger templates when you want to display certain elements only if a post, label, or data field matches something inside a list or condition.

Why Use Membership Operators?

Using membership operators like in or contains allows you to:

• Check if a label, keyword, or tag exists within a post.
• Display custom layouts for posts belonging to certain categories.
• Create conditional widgets based on whether a specific value is part of an array.
• Reduce repetitive <b:if> statements and simplify logic.
• Enable smart, data-driven templates that respond to user context or post data.

In other words, it gives you fine-grained control over your Blogger theme—without any external scripting.

Syntax of the Membership Operator

The membership operator comes in two forms: in and contains. Both check for membership, but they reverse the position of the operands. Let’s look at the general syntax below.

Name	Operator	Operands	Default Syntax	Result
In	in	2	{string} in {array[string]}	boolean
			{boolean} in {array[boolean]}
			{number} in {array[number]}
Contains	contains		{array[string]} contains {string}
			{array[boolean]} contains {boolean}
			{array[number]} contains {number}

Rules to Remember

• The operation always returns a Boolean value.
• The compared value must be the same type as the array’s elements (string, number, or boolean).
• The compared value can be:
• An explicit (hardcoded) value.
• A Blogger data variable (like data:post.title).
• A result from another nested Blogger expression.
• You can combine membership operations with other Boolean operators such as and, or, or not.

Practical Examples

Let’s see how the in and contains operators work in real Blogger conditions. These examples are simple and can be tested directly inside your Blogger template editor.

Example 1: Using the in Operator

<b:eval expr='"budi" in ["budi","ani","kaka budi"]'/>

Result: true
Explanation: The string “budi” exists inside the array, so the condition returns true. You could use this to trigger a specific widget or content block if the keyword “budi” is present.

Example 2: Using the contains Operator

<b:eval expr='["ani","ibu budi","bapak budi"] contains "budi"'/>

Result: false
Explanation: Although some elements contain the word “budi” as part of their text, they are not exact matches in the array. The contains operator only checks for a full match, not a substring.

Functional Syntax Alternative

Blogger also allows you to use functional syntax for the membership operator. This can be useful if your condition repeats the operator multiple times or if you want to write it in a cleaner, function-like structure.

in({string|number|boolean}, {array[string|number|boolean]})

contains({string|number|boolean}, {array[string|number|boolean]})

Example:

<b:eval expr='in("budi", ["budi","ani","kaka budi"])'/>

Same as before, this returns true since “budi” is present inside the array.

Advanced Use Cases in Blogger Templates

Let’s go beyond simple examples and see how you can actually apply membership operators in a Blogger template for more dynamic functionality.

1. Show or Hide Widgets Based on Labels

<b:if cond='data:post.labels contains &quot;Featured&quot;'>
  <div class="featured-post">This post is marked as featured!</div>
</b:if>

Use this snippet to display a widget or banner only for posts that have a specific label, such as “Featured” or “Tutorial.”

2. Highlight a Post Type Automatically

<b:if cond='data:post.labels contains &quot;Review&quot;'>
  <span class="badge-review">Review</span>
</b:if>

This will automatically show a badge or tag on posts labeled “Review.”

3. Check for Page Type and Add Custom Styles

<b:if cond='data:blog.pageType in ["index","archive"]'>
  <style>body { background-color:#fafafa; }</style>
</b:if>

You can style certain page types (like your homepage or archive pages) differently based on their data type value.

Common Mistakes and How to Fix Them

Even though the syntax looks simple, small errors can cause Blogger to misread your code. Here are some common issues:

• Using Wrong Quotes: Always use " inside Blogger conditions instead of plain quotes (“). Blogger XML requires proper encoding.
• Type Mismatch: Make sure you’re comparing strings with string arrays, not mixing with numbers or booleans.
• Expecting Partial Matches: Remember that in and contains require exact matches, not substrings.
• Array Syntax Errors: Double-check that your arrays are enclosed with [ ] and separated by commas.
• Forgetting Context: Some Blogger variables, such as data:post.labels, are arrays of objects. Make sure you access them properly.

Frequently Asked Questions (FAQ)

1. What’s the difference between in and contains?

in checks if a value exists inside an array. Meanwhile, contains checks if an array contains a specific value. They are essentially mirror forms of each other.

2. Is the membership operator case-sensitive?

Yes. The comparison is case-sensitive. “Budi” and “budi” are different. Use consistent casing or handle it via data normalization if needed.

3. Can I use these operators in custom widgets?

Absolutely. They’re perfect for conditional widgets, especially if you want to show or hide elements based on specific data like category, title, or URL.

4. Can I chain multiple conditions together?

Yes, you can use logical operators like and or or to combine multiple membership checks in one condition.

<b:if cond='"Tutorial" in data:post.labels or "Guide" in data:post.labels'>
  <div>This post is a tutorial or guide.</div>
</b:if>

Troubleshooting Tips

• If your condition isn’t working, test it with <b:eval> first to see what value it returns.
• Check for typos or invisible characters when copying code.
• Ensure you’re not comparing objects (like full label objects) directly—use string values instead.
• Use smaller test cases first before applying logic to your full template.

Conclusion

The membership operator (in / contains) is one of the simplest yet most powerful tools in Blogger template customization. By understanding how to use it properly, you can make your site more intelligent, efficient, and dynamic—whether it’s for conditionally displaying widgets, styling posts, or filtering specific page types.

Start small, test your logic carefully, and build up to more complex conditions as you grow comfortable with Blogger’s XML expressions. Mastering these operators will make your Blogger templates feel more like coded web apps than static blogs.

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Final Thoughts: I hope this article helped you understand how to use the Blogger Membership Operators. If you found it useful, don’t forget to bookmark this post or share it with fellow Blogger creators. Keep learning, keep experimenting—and happy coding!