"Expression Expected" in EJS: Demystifying the Error and Finding Solutions
Are you trying to inject dynamic content into your HTML using EJS (Embedded JavaScript Templates) and encountering the dreaded "Expression Expected" error? Don't fret, this common issue can be easily resolved. This article will guide you through understanding the error, pinpointing its cause, and offering practical solutions to get your EJS templates working smoothly.
Understanding the Error
The "Expression Expected" error in EJS signifies that the template engine is unable to interpret the code it's trying to execute. It's essentially saying, "I need something to calculate or evaluate, but you haven't given me anything to work with!" This usually arises when you're attempting to embed JavaScript code within your EJS template, but you've made a syntax mistake.
The Scenario: EJS within <script> Tags
Let's imagine a simple scenario: you're trying to include a script tag in your EJS template and want to dynamically generate its content:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>EJS Example</title>
</head>
<body>
<script>
console.log("Hello from EJS!");
</script>
</body>
</html>
This code will likely trigger the "Expression Expected" error. Why? Because EJS expects to find an expression (a piece of code that evaluates to a value) within its delimiters (<%= %>). The code inside the <script> tag is interpreted as regular JavaScript by the browser, not by the EJS engine.
Pinpointing the Problem
The root of the issue lies in the improper use of EJS delimiters within the <script> tag. EJS is designed to handle dynamic content within the HTML structure, not within JavaScript code blocks.
Solution 1: Separate JavaScript Logic
The most common and recommended approach is to separate your JavaScript logic from your EJS template. Define your JavaScript functions in a separate .js file and include it in your HTML. This keeps your code organized and ensures that EJS focuses on rendering the HTML structure.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>EJS Example</title>
<script src="script.js"></script>
</head>
<body>
</body>
</html>
// script.js
console.log("Hello from JavaScript!");
Solution 2: Use EJS Expressions for Dynamic Values
If you need to inject dynamic values within a <script> tag, you can use EJS expressions. For example, you can pass a variable from your EJS template to the JavaScript code:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>EJS Example</title>
</head>
<body>
<script>
const message = "<%= myVariable %>";
console.log(message);
</script>
</body>
</html>
In your EJS template, myVariable would be defined with the value you want to pass to the script:
<% myVariable = 'Hello from EJS!' %>
This approach allows you to dynamically control specific values within your JavaScript code.
Additional Considerations
- Escape HTML: Remember to escape any user-provided content within your
<script>tag to prevent XSS vulnerabilities. - Performance: When handling large amounts of data, consider optimizing your template structure and data handling to enhance performance.
Conclusion
The "Expression Expected" error in EJS usually stems from the misuse of delimiters within JavaScript blocks. By adhering to the proper separation of concerns and utilizing EJS expressions strategically, you can avoid this error and maintain a clean and efficient codebase.
For more detailed information on EJS and its capabilities, refer to the official EJS documentation https://ejs.co/.
