Summarized
Your attempt to utilize victor as if it were an ECMAScript 6 module is incorrect. Two possible solutions are:
Have tsc transform your modules to a format like commonjs, which will handle the necessary connection between victor and your code.
Alternatively, load your application through a module loader that can provide the required integration.
Explanatory Details
With the import you've specified, running the latest version of tsc yields the error:
This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
Enabling esModuleInterop resolves this issue. Check out the test code I employed:
import Victor from "victor";
const foo = new Victor(1, 2);
console.log(foo.y);
Here's the corresponding tsconfig.json:
{
"compilerOptions": {
"esModuleInterop": true
}
}
The problem stems from the fact that when using import Victor from "victor", you're requesting the value exported through an export default... statement based on ES6 modules syntax. However, no such equivalent exists in victor. Hence, there needs to be something to bridge the gap. Upon compilation, tsc generates the following code snippet:
"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
return (mod && mod.__esModule) ? mod : { "default": mod };
};
exports.__esModule = true;
var victor_1 = __importDefault(require("victor"));
var foo = new victor_1["default"](1, 2);
console.log(foo.y);
An essential point to note here is the __importDefault helper function that addresses how TS accesses what a module exports as export default.... For ES6 modules, this process favors correctly structured defaults, while for non-ES6 modules, the helper creates a pseudo-module with the original module's default export.
When targeting ECMAScript modules with this tsconfig.json:
{
"compilerOptions": {
"esModuleInterop": true,
"module": "es6"
}
}
The resulting emitted code becomes:
import Victor from "victor";
var foo = new Victor(1, 2);
console.log(foo.y);
Omitting the helper function implies reliance on the module loader to replicate the logic integrated by __importDefault. Renaming the file extension to mjs and executing:
$ node --experimental-modules test.mjs
Returns the output:
(node:18394) ExperimentalWarning: The ESM module loader is experimental.
2
In situations involving Node with experimental module support, similar functionality akin to __importDefault is provided.
Mere usage of allowSyntheticDefaultImports sans esModuleInterop shifts the responsibility onto you to ensure another tool within your toolchain fulfills the duties of __importDefault. Compiler offers no assistance in this scenario and lets you progress under the assumption that the task will be handled elsewhere.