Passing parameters in a URL can be very useful for web applications. It allows you to pass data between pages without requiring forms or sessions. In this article, we’ll explore the basics of passing URL parameters, also known as query string parameters.
What are Query String Parameters?
Query string parameters are additional values appended to a URL that can contain data. They are typically used to pass information from one page to another. The parameters are added after a “?” in the URL and are formatted as key-value pairs, like this:
http://example.com/page?key1=value1&key2=value2
In this example, there are two parameters – key1 with a value of value1 and key2 with a value of value2. These can be retrieved and used by the receiving page to perform actions or display data.
Key Things to Know
- Parameters come after the ? and are separated by &
- Each parameter has a key and value separated by =
- Keys and values are encoded to be URL friendly
- Order of parameters does not matter
- Parameters are appended to the end of the URL
Why Use Query Parameters?
There are a few key reasons to use query string parameters:
- Pass data between pages – You can pass values and data to another page to use
- Modify content – Parameters can be used to customize or filter content
- Track behavior – Useful for analytics and tracking codes
- No server load – Simple way to pass data without loading server
- Bookmarkable URLs – Parameters can be bookmarked for later
Overall, query parameters provide an easy way to pass data between pages without reloading the server. They can help create customizable and dynamic web applications.
How to Format Query Parameters
Query string parameters follow a specific formatting convention:
- Start after ? in the URL
- Use & to separate multiple parameters
- Format as key=value pairs
- Keys should not have spaces or special characters
- Values must be URL encoded
Here is an example with two parameters:
http://example.com/page?key1=value1&key2=value2
To add more parameters, just append additional &key=value pairs:
http://example.com/page?key1=value1&key2=value2&key3=value3
Encoding Values
Since URLs cannot contain spaces or special characters, the parameter values need to be URL encoded. This converts them into a URL friendly format.
For example, spaces would be converted to %20. Encoding ensures the URL will work correctly.
http://example.com?name=John%20Doe
There are many online tools available to URL encode values if needed.
Accessing Query String Parameters
To access the query string parameters, you need to parse them from the URL on the receiving page. This will depend on what language or framework you are using.
JavaScript
In JavaScript, you can access the current URL query string using:
const queryString = window.location.search;
This will return a string like ?key1=value1&key2=value2. You can then use the split() method and other String functions to parse the parameters into key/value pairs.
PHP
In PHP, the query string is available in $_GET. This will contain an associative array of all the query parameters. For example:
$key1 = $_GET['key1']; $key2 = $_GET['key2'];
You can loop through $_GET to get all query string values.
Python
For Python and Flask, the request.args object contains the query parameters:
from flask import request key1 = request.args.get('key1') key2 = request.args.get('key2')
This allows accessing query parameters in Python web apps.
Ruby on Rails
In Ruby on Rails, the params hash contains the query string data. For example:
key1 = params[:key1] key2 = params[:key2]
The Rails params helper provides easy access in Ruby web apps.
Most frameworks and languages provide simple ways to access URL parameters that are passed. Consult the documentation for your specific stack.
Passing Data with Query Parameters
Now that we can access URL query string data, let’s look at some examples of passing data between pages.
Filter Content
You can use parameters to filter content on a page. For example, on a search page you could add a “category” parameter:
http://example.com/search?category=books
The receiving page would access this category value and filter the search results accordingly.
Forms and Data
Query parameters are often used to send form data. For example, a contact form may send data like:
http://example.com/contact?name=John&message=Hello
This submits the form values to the contact page which can process it.
User IDs
You can pass a user id or other identifier to customize pages. For example:
http://example.com/profile?user=253
This allows loading the profile data for user 253 dynamically.
Tracking and Analytics
Query parameters can also be used for tracking and analytics. Pages often append IDs like:
http://example.com/page?utm_source=newsletter&utm_campaign=summer
This allows tracking traffic sources and campaigns for analytics.
Best Practices
When working with query parameters, here are some best practices:
- Use descriptive, understandable keys – Avoid vague names like p1, p2
- Keep parameters short and concise
- Encode special characters and spaces in values
- Validate and sanitize input for security
- Consider length limits and overlong URLs
- Use params only for non-sensitive public data
Keeping parameters simple, secure and URL-friendly will create the most stable experience.
Libraries and Tools
There are many helpful client-side and server-side libraries for working with query parameters:
Client-Side
- jQuery – url(), param()
- Lodash – get()
- qs – Parse and stringify
Server-Side
- Express – req.query
- Django – request.GET
- Rails – Params helper
- Laravel – Input::get()
These libraries make it even easier to work with query parameters in web applications.
Limitations
There are a few limitations to consider when using query parameters:
- Length limits – URLs have a maximum total length
- Can’t send private/sensitive data – Query params are visible in the URL
- Hard to manage many parameters – The URL can get long and messy
- Requires encoding – Need to encode special characters
For large or complex data, POST requests or sessions may be more appropriate.
Security Considerations
Since query parameters are exposed in the URL, there are some security factors to consider:
- Sanitize and validate all parameters – Escape, trim, type check
- Avoid sensitive user data – Anyone can see the URL query values
- Use POST for forms whenever possible
- Restrict parameter values if needed
- Limit parameter length and total URL size
Parameter pollution and overlong URLs can be used in denial of service attacks. Input validation helps mitigate risks.
Summary
Query string parameters provide a simple way to pass data between web pages and HTTP requests. By appending key/value pairs after the URL, you can build dynamic and customizable web applications.
Keep these key points in mind:
- Format parameters as key=value pairs after ?
- Access parameters through request objects in code
- Use for non-sensitive public data only
- Validate and sanitize all user input
- Encode spaces and special characters
With proper security precautions, query parameters unlock many possibilities for web developers.
Frequently Asked Questions
How many query parameters can a URL have?
There is no set limit on the number of query parameters in a URL, however there is a general length limit of 2000-8000 characters depending on the browser. Best practice is to keep the number and size of parameters reasonably small for usability.
Should query parameters be used for sensitive data?
No, sensitive user data like passwords, financial data, or personal details should not be passed as query parameters since they are exposed in the URL. POST requests are more appropriate for this.
What are some other names for query parameters?
Query string parameters are also sometimes referred to as:
- GET parameters
- URL variables
- URL parameters
- Query vars
How are multiple query parameters delimited?
Multiple parameters in a query string are delineated using the & symbol. For example: page1.html?param1=value1¶m2=value2. The & separates each key/value pair.
Can query parameters be used with any HTTP method?
Query parameters are most commonly associated with GET requests. However, they can also be used with POST in some frameworks if configured to process the params. They apply specifically to the query string section of the URL.
Example Passing Data with Query Parameters
Let’s look at a full example of passing data between two pages using URL query parameters.
We have a search page that displays book results. We want to pass the search term to the results page in order to filter and display the matching books.
Search Page
Our search page has a form with a text input to enter a search term. When the form is submitted, we redirect to the results page and append a query parameter for the search term.
<form action="results.html"> <input type="text" name="searchterm"> <button type="submit">Search</button> </form>
This will redirect to a URL like:
results.html?searchterm=harry+potter
Results Page
On the results page, we can access the search term parameter:
// Get search term const term = new URLSearchParams(window.location.search).get('searchterm'); // Filter books by search const results = filterBooks(term); // Display results displayBooks(results);
By reading the term from the URL, we can dynamically filter and display the correct book results!
This is a simple example of passing data between two pages with query parameters. The concept can be applied to many types of web applications.
Conclusion
Query string parameters provide a very useful way to pass customizable data between web pages. By appending key/value pairs to the end of a URL, you can build more dynamic and interactive web applications.
They make it easy to pass data without requiring server requests or client-side storage. Just remember to validate and sanitize input for security.
For small public data like IDs, filters, options, etc, query parameters are a great choice. Use them wisely as part of your web development toolbox.