Jest, being a widely-used JavaScript testing framework, provides various features to facilitate the testing process. One of the features that often confuses developers is the difference between `global` and `globalThis`. Understanding the distinction between these two is crucial for writing effective tests and ensuring that your code works as expected across different environments.
In Jest, `global` and `globalThis` are both objects that provide access to global variables and functions. However, there are some key differences between the two that you should be aware of.
Firstly, `global` is an object that is accessible within Jest test files. It is essentially a wrapper around the `window` object in a browser environment and the `global` object in a Node.js environment. This means that if you are testing a browser-based application, `global` will give you access to the browser’s global variables and functions, such as `window`, `document`, and `navigator`. Similarly, in a Node.js environment, `global` will provide access to Node.js-specific global variables and functions, like `process` and `console`.
On the other hand, `globalThis` is a newer, standardized way to access the global object in JavaScript. It is defined by the ECMAScript Internationalization API (ECMA-402) and is supported in all modern browsers and Node.js environments. The `globalThis` object provides a consistent way to access the global object across different environments, making it a more portable option than `global`.
One of the main differences between `global` and `globalThis` is their scope. `global` is only available within Jest test files, while `globalThis` is available globally in your JavaScript code. This means that you can use `globalThis` in your test files as well as in your application code, ensuring that you have a consistent way to access the global object.
Another difference is that `global` is not part of the ECMAScript specification, while `globalThis` is. This makes `globalThis` a more future-proof option, as it is likely to be supported in all JavaScript environments moving forward.
Here’s an example to illustrate the difference between `global` and `globalThis`:
“`javascript
// Using global in a Jest test file
describe(‘Global object’, () => {
it(‘should have access to the window object’, () => {
expect(global.window).toBeDefined();
});
});
// Using globalThis in a Jest test file
describe(‘GlobalThis object’, () => {
it(‘should have access to the window object’, () => {
expect(globalThis.window).toBeDefined();
});
});
“`
In the above example, both `global` and `globalThis` are used to access the `window` object within a Jest test file. As you can see, the output is the same, but the underlying object being accessed is different.
In conclusion, while both `global` and `globalThis` provide access to the global object in JavaScript, there are some important differences between the two. Understanding these differences will help you write more effective tests and ensure that your code works consistently across different environments.
