Weird Javascript behaviour, when combined with ejs Objects

2 min read 28-09-2024

Weird Javascript behaviour, when combined with ejs Objects

JavaScript is a versatile programming language, but its behavior can sometimes be puzzling, especially when combined with EJS (Embedded JavaScript) templating. This article will delve into some common quirks that developers may face while using JavaScript with EJS objects, providing clarity and practical solutions.

The Problem Scenario

When using EJS to render HTML templates, developers may encounter unexpected behavior with JavaScript objects. For instance, consider the following code snippet:

const user = {
  name: "John",
  age: 30,
  isAdmin: false
};

// EJS template usage
<% if (user.isAdmin) { %>
  <h1>Welcome, Admin <%= user.name %></h1>
<% } else { %>
  <h1>Welcome, User <%= user.name %></h1>
<% } %>

In this example, the intention is to check if the user is an admin and display an appropriate welcome message. However, you might run into issues when rendering this template, particularly if there are changes made to the user object elsewhere in your code.

Analysis of the Behavior

One potential source of confusion arises from JavaScript's handling of objects, especially when they are passed around in different contexts. Objects in JavaScript are reference types; when you pass an object to a function or manipulate it in a different scope, you're working with a reference to that original object. This can lead to unexpected changes if the object is modified inadvertently, impacting the EJS rendering.

Example of Unexpected Changes

// Original object
const user = {
  name: "John",
  age: 30,
  isAdmin: false
};

// Function that modifies user object
function updateUser(newData) {
  Object.assign(user, newData);
}

// Updating user object
updateUser({ isAdmin: true });

// EJS rendering
<% if (user.isAdmin) { %>
  <h1>Welcome, Admin <%= user.name %></h1>
<% } else { %>
  <h1>Welcome, User <%= user.name %></h1>
<% } %>

In this case, because we modified the original user object within the updateUser function, the output of the EJS template will reflect this change, leading to the message "Welcome, Admin John". If developers are unaware that the user object has been modified, they may be puzzled by the output.

Solutions and Best Practices

To mitigate such weird behaviors, consider the following best practices:

Clone Objects: Before passing an object that may undergo changes, create a clone to prevent unintended side effects. You can use methods like Object.assign or the spread operator.
```
const clonedUser = { ...user };
```
Immutability: Leverage immutable data structures or libraries like Immutable.js or Immer. This will ensure that your objects remain unchanged unless explicitly updated.
Explicit Checks: Always check the values of your objects before rendering in EJS. This can help you catch unexpected modifications early.
Use Consistent Naming Conventions: Maintain clarity on what objects are being used, especially if similar names are reused in different scopes. This can help prevent confusion and inadvertent errors.

Additional Resources

Conclusion

While JavaScript's dynamic nature allows for powerful coding practices, it can also lead to confusion when combined with EJS templating. By understanding how objects are referenced and modified, developers can avoid unexpected behaviors and create more reliable applications. Always prioritize clarity, immutability, and consistent coding practices to ensure a smoother development experience.

Remember, the nuances of JavaScript can be challenging, but with practice and attention to detail, you can navigate them effectively!