Solving the Node.js EJS Variable Not Defined Issue: A Comprehensive Guide

If you’re reading this, chances are you’re stuck with the frustrating Node.js EJS variable not defined issue. Don’t worry, you’re not alone! Many developers have been in your shoes, and with this article, we’ll help you overcome this hurdle and get back to building amazing applications.

What is EJS and How Does it Work with Node.js?

EJS (Embedded JavaScript) is a templating engine that allows you to generate HTML templates using JavaScript. It’s a popular choice for Node.js applications because of its simplicity and flexibility. EJS works by allowing you to embed JavaScript code within your HTML templates, making it easy to dynamically generate content.

When you use EJS with Node.js, you can render templates by passing data to the EJS engine, which then replaces placeholders with actual values. This process is called rendering. The rendered HTML is then sent to the client’s browser, where it’s displayed to the user.

The Node.js EJS Variable Not Defined Issue

So, what happens when you try to render an EJS template, but the variables you’re trying to access are not defined? You get an error message that looks something like this:

ReferenceError: Variable 'variableName' is not defined
at eval (eval at compile (/path/to/ejs.js:573:12))
at compile (/path/to/ejs.js:573:12)
at Object.exports.render (/path/to/ejs.js:363:10)
at /path/to/your/app.js:23:11
at Layer.handle_error (/path/to/express.js:324:18)
at next (/path/to/express.js:1657:11)
at /path/to/express.js:1695:5
at Layer.handle_request (/path/to/express.js:1625:5)
at next (/path/to/express.js:1657:9)

This error message is telling you that the variable you’re trying to access is not defined. But why is that? You’ve defined the variable in your Node.js script, so why can’t EJS see it?

Understanding Scope in Node.js and EJS

The reason you’re getting this error is due to scope. In Node.js, variables are scoped to the current module or function. When you render an EJS template, the template engine has its own scope, which is separate from your Node.js script.

This means that variables defined in your Node.js script are not automatically available to your EJS template. You need to explicitly pass the variables to the EJS engine as an object, which is then used to render the template.

Solving the Node.js EJS Variable Not Defined Issue

Now that we understand the root cause of the issue, let’s explore some solutions to get you up and running again.

Passing Variables to EJS

The simplest way to solve the variable not defined issue is to pass the variables as an object to the EJS engine. Here’s an example:

const express = require('express');
const app = express();
const ejs = require('ejs');

app.get('/', (req, res) => {
  const name = 'John Doe';
  const age = 30;

  const data = { name, age };
  const html = ejs.renderFile('template.ejs', data);
  res.send(html);
});

In this example, we define two variables, `name` and `age`, and create an object called `data` to hold these variables. We then pass the `data` object to the EJS engine using the `renderFile` method.

In your EJS template, you can access the variables like this:

<h1><%= name %></h1>
<p>Age: <%= age %></p>

Using Middleware to Pass Variables to EJS

Another approach is to use middleware to pass variables to EJS. Middleware functions are functions that have access to the entire request object and can modify it before passing it to the next middleware function or the route handler.

You can use middleware to attach variables to the request object, which can then be accessed in your EJS template. Here’s an example:

const express = require('express');
const app = express();
const ejs = require('ejs');

app.use((req, res, next) => {
  req.data = { name: 'John Doe', age: 30 };
  next();
});

app.get('/', (req, res) => {
  const html = ejs.renderFile('template.ejs', req.data);
  res.send(html);
});

In this example, we define a middleware function that attaches an object called `data` to the request object. This object contains the variables we want to pass to EJS. We then access these variables in our EJS template using the `req.data` object:

<h1><%= req.data.name %></h1>
<p>Age: <%= req.data.age %></p>

Using a Template Engine with Support for Node.js Scope

Another solution is to use a template engine that has built-in support for Node.js scope. One popular option is Pug. Pug is a high-performance template engine that allows you to access Node.js variables directly in your templates.

Here’s an example:

const express = require('express');
const app = express();
const pug = require('pug');

app.set('view engine', 'pug');

app.get('/', (req, res) => {
  const name = 'John Doe';
  const age = 30;

  res.render('template', { name, age });
});

In this example, we set Pug as our template engine and define two variables, `name` and `age`. We then pass these variables to the Pug engine using the `res.render` method.

In our Pug template, we can access the variables directly:

h1= name
p Age: #{age}

Best Practices for Avoiding the Node.js EJS Variable Not Defined Issue

To avoid running into the Node.js EJS variable not defined issue, follow these best practices:

• Always pass variables to EJS as an object.
• Use middleware to attach variables to the request object.
• Use a template engine with built-in support for Node.js scope, such as Pug.
• Avoid using global variables, as they can lead to scope issues.
• Keep your variables and templates organized, and use meaningful names to avoid confusion.

Conclusion

The Node.js EJS variable not defined issue can be frustrating, but with the right approach, you can overcome it. By passing variables to EJS as an object, using middleware, or switching to a template engine with built-in Node.js scope support, you can ensure that your variables are accessible in your EJS templates.

Remember to follow best practices, keep your code organized, and always test your applications thoroughly to avoid running into issues. With these strategies, you’ll be well on your way to building robust and scalable Node.js applications with EJS.

Template Engine	Support for Node.js Scope
EJS	No
Pug	Yes
Handlebars	No

Frequently Asked Question

Get stuck with undefined variables in your EJS templates? Fret not, we’ve got you covered!

Let me know if you need anything else!