Differentiating between module-level variables and local variables in TypeScript

Question

Differentiating between module-level variables and local variables in TypeScript

Check out this module:

export module Example{
    let client : any;

    export function myExample(customer: string) {
        // How can I access the variable "client" at the module level inside this function?
        // Should I consider using Pascal Case for module-level variables to avoid conflicts like this?
    }
}

The customer in the myExample function is a string. How do I refer to the module-level client?

If it were a class, I could use this.customer, but that doesn't work in a module context. Also, Example.customer won't work unless the customer variable is exported...

typescript typescript1.8

Answer 1

Answer №1

Typically, modules will export classes, functions, or other elements such as enums.

In this specific case, the export module Example is defining Example as a namespace. This means that any mention of the myExample function must be preceded by the namespace, like so: Example.myExample().

You are correct in noting that customer is not accessible unless it is exported. This limitation exists because export module Example solely denotes a namespace and does not export variables or classes.

It's puzzling why you would opt for export module instead of using export class:

export class Example2 {
    customer: string = 'Example2.customer';
    myExample(customer: string) {
        console.log(`Example ${this.customer}`);
        console.log(`Example ${customer}`);
    }
}

This class essentially acts as a module due to the presence of the export keyword.

Answer 2

Typically, modules will export classes, functions, or other elements such as enums.

In this specific case, the export module Example is defining Example as a namespace. This means that any mention of the myExample function must be preceded by the namespace, like so: Example.myExample().

You are correct in noting that customer is not accessible unless it is exported. This limitation exists because export module Example solely denotes a namespace and does not export variables or classes.

It's puzzling why you would opt for export module instead of using export class:

export class Example2 {
    customer: string = 'Example2.customer';
    myExample(customer: string) {
        console.log(`Example ${this.customer}`);
        console.log(`Example ${customer}`);
    }
}

This class essentially acts as a module due to the presence of the export keyword.

Answer 3

Answer №2

Below is the JS version of the TS question generated by JavaScript:

define(["require", "exports"], function (require, exports) {
    "use strict";
    var Example;
    (function (Example) {
        var customer;
        function myExample(customer) {
            // How can I access the module level customer object here?
            // Should module level variables be Pascal Case to avoid this conflict?
        }
        Example.myExample = myExample;
    })(Example = exports.Example || (exports.Example = {}));
});

Because customer is not exported, it remains private. As a result, regular JavaScript variable scoping rules apply and accessing the module level customer becomes impossible. An effective solution (and a common convention for module level private variables) is to prefix the outer most customer with an underscore:

export module Example{
    let _customer : any;

    export function myExample(customer: string) {
        _customer = customer;
    }
}

Answer 4

Below is the JS version of the TS question generated by JavaScript:

define(["require", "exports"], function (require, exports) {
    "use strict";
    var Example;
    (function (Example) {
        var customer;
        function myExample(customer) {
            // How can I access the module level customer object here?
            // Should module level variables be Pascal Case to avoid this conflict?
        }
        Example.myExample = myExample;
    })(Example = exports.Example || (exports.Example = {}));
});

Because customer is not exported, it remains private. As a result, regular JavaScript variable scoping rules apply and accessing the module level customer becomes impossible. An effective solution (and a common convention for module level private variables) is to prefix the outer most customer with an underscore:

export module Example{
    let _customer : any;

    export function myExample(customer: string) {
        _customer = customer;
    }
}

Differentiating between module-level variables and local variables in TypeScript

Answer №1

Answer №2

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