Explain “export =” and “export as namespace” syntax in TypeScript

The first form is used for CommonJS and AMD module systems. You have to match the export = React with import React = require('./React')

See the documentation which gives this example:

ZipCodeValidator.ts

let numberRegexp = /^[0-9]+$/;
class ZipCodeValidator {
    isAcceptable(s: string) {
        return s.length === 5 && numberRegexp.test(s);
    }
}
export = ZipCodeValidator;

Test.ts

import zip = require("./ZipCodeValidator");

// Some samples to try
let strings = ["Hello", "98052", "101"];

// Validators to use
let validator = new zip();

// Show whether each string passed each validator
strings.forEach(s => {
  console.log(`"${ s }" - ${ validator.isAcceptable(s) ? "matches" : "does not match" }`);
});

The export as namespace form creates a global variable so it can be used without importing, but you may still import it with the import { name } from "some-library" form of import. See the documentation which gives this example:

math-lib.d.ts

export const isPrime(x: number): boolean;
export as namespace mathLib;

The library can then be used as an import within modules:

import { isPrime } from "math-lib";
isPrime(2);
mathLib.isPrime(2); // ERROR: can't use the global definition from inside a module

It can also be used as a global variable, but only inside of a script. (A script is a file with no imports or exports.)

mathLib.isPrime(2);

Here you have a generic type library which doesn’t know which module system is being used so it tries to cover all bases.