Global Declarations in TypeScript: How to Declare Global Variables and Functions
TypeScript is a superset of JavaScript that provides optional static typing, classes, and interfaces. It helps developers write more maintainable and scalable code. One of TypeScript's features is the ability to declare global variables and functions.
In this post, we'll look at how to declare global variables and functions in TypeScript and why you might want to do so.
When you declare a variable or function in TypeScript, it's scoped to the file or module in which it's declared. This means that other files or modules cannot access it unless it's exported.
However, there are situations where you may want to declare a variable or function that's accessible across your entire application. This is where global declarations come in.
A global declaration is a variable or function that's accessible across your entire application, regardless of the file or module in which it's declared. To declare a global variable or function in TypeScript, you use the declare
keyword.
Here's an example of how to declare a global variable in TypeScript:
declare var myGlobalVariable: string;
In this example, we're declaring a global variable called myGlobalVariable
of type string
. We're not providing a value for the variable, as it will be initialized elsewhere in our application.
Similarly, here's an example of how to declare a global function in TypeScript:
declare function myGlobalFunction(): void;
In this example, we're declaring a global function called myGlobalFunction
that takes no arguments and returns void
.
Once you've declared a global variable or function, you can use it anywhere in your application. Here's an example of how to use the global variable we declared earlier:
myGlobalVariable = "Hello, world!";
console.log(myGlobalVariable);
In this example, we're assigning the value "Hello, world!"
to myGlobalVariable
and then logging it to the console.
Here's an example of how to use the global function we declared earlier:
myGlobalFunction();
In this example, we're calling myGlobalFunction
.
You might be wondering why you would want to use global declarations in TypeScript. After all, TypeScript encourages you to write modular code that's scoped to individual files or modules.
However, there are situations where global declarations can be useful. For example:
In these situations, global declarations can help you write cleaner, more maintainable code.
window
object in TypeScript. For example:declare global {
interface Window {
myGlobalVariable: string;
myGlobalFunction: () => void;
}
}
This syntax declares the myGlobalVariable
and myGlobalFunction
properties on the window
object, making them accessible globally.
In this post, we've looked at how to declare global variables and functions in TypeScript using the declare
keyword. We've also discussed why you might want to use global declarations in your TypeScript applications.
By using global declarations, you can write cleaner, more maintainable code that's easier to work with across multiple files or modules.