When do we use typescript import * as?

Not really an answer, but a usage: Consider you have a few constant strings to be used in your application, you can define them in a single file and export

export const name = "NAME";
export const someOtherString = "SOME_CONST_STRING";

Then you can import them in a single variable using:

import * as CONST_STRINGS from './yourFilePath';

and use as

CONST_STRINGS.name 
CONST_STRINGS.someOtherString

From the TypeScript doc:

Import the entire module into a single variable, and use it to access the module exports

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The example code imports all exports of the stacktrace-js module into a variable called StackTrace.

Any named exports will be available as properties of the same name.

If the module has a default export it will be available as the default property.

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Note also from the TypeScript Module doc:

Starting with ECMAScript 2015, JavaScript has a concept of modules. TypeScript shares this concept.

So TypeScript modules behave in the same way as ES6 JavaScript modules.

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You would use import * as in either TypeScript or JavaScript when you want access to all of the module exports in a single variable.