Default exports

Each module can optionally export a default export. Default exports are marked with the keyword default; and there can only be one default export per module. default exports are imported using a different import form.

default exports are really handy. For instance, a library like JQuery might have a default export of jQuery or $, which we’d probably also import under the name $ or jQuery.

JQuery.d.ts

declare let $: JQuery;
export default $;

App.ts

import $ from "JQuery";

$("button.continue").html( "Next Step..." );

Classes and function declarations can be authored directly as default exports. Default export class and function declaration names are optional.

ZipCodeValidator.ts

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

Test.ts

import validator from "./ZipCodeValidator";

let myValidator = new validator();

StaticZipCodeValidator.ts

const numberRegexp = /^[0-9]+$/;

export default function (s: string) {
  return s.length === 5 && numberRegexp.test(s);
}

Test.ts

import validate from "./StaticZipCodeValidator";

let strings = ["Hello", "98052", "101"];

// Use function validate
strings.forEach(s => {
  console.log(`"${s}" ${validate(s) ? " matches" : " does not match"}`);
});

default exports can also be just values:

OneTwoThree.ts

export default "123";

Log.ts

import num from "./OneTwoThree";

console.log(num); // "123"

Links:

https://www.typescriptlang.org/docs/handbook/modules.html#default-exports

doc_TypeScript

2016-10-04 19:25:09

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