Javascript Express Error: Route.get() requires a callback function but got a [object]
Resolving 'Route.get() requires a callback function' Error in Express.js
Understanding Express.js
Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. It facilitates the rapid development of Node-based web applications by providing a simple interface to create routes, handle requests, and manage middleware.
For more information, visit the official Express.js website.
Identifying the Symptom
When working with Express.js, you might encounter the following error message:
Error: Route.get() requires a callback function but got a [object]
This error indicates that there is an issue with how a route handler is defined in your Express application.
Understanding the Issue
The error occurs when a non-function value is passed as a route handler in Express.js. Each route in Express requires a callback function that defines what should happen when a particular route is accessed. If an object or any other non-function value is mistakenly passed, Express will throw this error.
Common Mistake
A common mistake is passing an object or a variable that is not a function as the route handler. For example:
app.get('/example', { key: 'value' });
In the above example, an object is passed instead of a function.
Steps to Fix the Issue
To resolve this error, ensure that the route handler is a valid function. Follow these steps:
Step 1: Review Route Definitions
Check your route definitions to ensure that each route is associated with a function. For example:
app.get('/example', function(req, res) {
res.send('Hello World');
});
In this example, a function is correctly passed as the route handler.
Step 2: Verify Function Existence
If you are using a named function, ensure that the function is defined before it is used as a route handler:
function exampleHandler(req, res) {
res.send('Hello World');
}
app.get('/example', exampleHandler);
Step 3: Check for Typos
Ensure there are no typos in the function name or the way it is referenced in the route definition.
Conclusion
By ensuring that each route in your Express.js application is associated with a valid function, you can avoid the 'Route.get() requires a callback function' error. For further reading, check out the Express.js routing guide.
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