gilamran gilamran - 13 days ago 8
Javascript Question

Are ES6 module imports hoisted?

I know that in the new ES6 module syntax, the JavaScript engine will not have to evaluate the code to know about all the imports/exports, it will only parse it and “know” what to load.

This sounds like hoisting. Are the ES6 modules hoisted? And if so, will they all be loaded before running the code?

Is this code possible?

import myFunc1 from 'externalModule1';

myFunc2();

if (Math.random()>0.5) {
import myFunc2 from 'externalModule2';
}

Answer

After doing some more research, I've found:

  • Imports ARE hoisted! according to the spec of ModuleDeclarationInstantiation
  • ALL the dependent Modules will be loaded before running any code.

This code will have no errors, and will work:

localFunc();

import {myFunc1} from 'mymodule';

function localFunc() { // localFunc is hoisted
    myFunc1();
}