When working with EJS (Embedded JavaScript) for rendering HTML, developers occasionally face a specific issue: "Cannot pass collection into EJS file (HTML script tab specifically)." This problem often arises when trying to utilize a collection or an array in the <script> tag of an EJS file. In this article, we’ll break down the problem, share an example code that reflects the issue, and provide a solution along with practical explanations.
Original Code Example
Consider the following example where we attempt to pass a collection of data to an EJS file:
// Express.js route
app.get('/data', (req, res) => {
const myCollection = [{ name: 'Item 1' }, { name: 'Item 2' }, { name: 'Item 3' }];
res.render('template', { collection: myCollection });
});
In the corresponding EJS file (template.ejs), we might try to render this collection inside a <script> tag like this:
<!DOCTYPE html>
<html>
<head>
<title>My Page</title>
</head>
<body>
<h1>Data from Collection</h1>
<script>
var data = <%= JSON.stringify(collection) %>;
console.log(data);
</script>
</body>
</html>
The Issue Explained
The error message signifies that there is a challenge in how the collection is handled when trying to embed it within a script tag. A common issue arises from the use of <%= %> or <%- %> tags in EJS, which can sometimes lead to unescaped HTML characters or JavaScript syntax errors.
Solution and Best Practices
To successfully embed a collection into a script tag in EJS, we can utilize JSON.stringify() to safely serialize the collection into a JSON format that JavaScript can understand. This is crucial for passing arrays or objects.
Here’s the revised version of our EJS code that avoids common pitfalls:
<!DOCTYPE html>
<html>
<head>
<title>My Page</title>
</head>
<body>
<h1>Data from Collection</h1>
<script>
var data = <%= JSON.stringify(collection) %>;
console.log(data); // This will output: [Object, Object, Object]
</script>
</body>
</html>
Additional Explanation
-
Escaping: When using EJS tags, ensure to escape the data properly to avoid XSS (Cross-Site Scripting) vulnerabilities. Using
JSON.stringify()helps to achieve that by converting the JavaScript object into a safe JSON string. -
Logging and Debugging: For debugging purposes, you can console log the variable as shown above. This is useful to confirm that your data was correctly passed and is in the expected format.
-
Dynamic Data Rendering: This method of passing collections into script tags is useful when you need to handle dynamic data for front-end frameworks like React or Angular, where data is often manipulated on the client side.
Practical Example: Using the Data
Once we have successfully embedded the collection into the JavaScript variable, we can utilize it to dynamically generate HTML elements:
<body>
<h1>Data from Collection</h1>
<ul id="item-list"></ul>
<script>
var data = <%= JSON.stringify(collection) %>;
var itemList = document.getElementById('item-list');
data.forEach(function(item) {
var li = document.createElement('li');
li.textContent = item.name;
itemList.appendChild(li);
});
</script>
</body>
Conclusion
In conclusion, the issue of not being able to pass collections into an EJS file, particularly in the context of the HTML <script> tag, can be resolved through careful data handling and serialization using JSON.stringify(). By following best practices for escaping and rendering dynamic data, you can effectively leverage EJS for your web applications.
Useful Resources
By applying these techniques, you can enhance the functionality of your web applications and avoid common pitfalls associated with data rendering in EJS. Happy coding!
