javascript: modifing an imported 'variable' causes 'Assignment to constant variable' even it is not a constant

Question

I have two files, file1 exports a variable 'not a constant' var x=1 and file2 which imports this variable from it

the problem is that I canno't modify that imported variable even it is not a constant!

file1.js

export var x=1 //it is defined as a variable not a constant

file2.js

import {x} from 'file1.js'
console.log(x) //1
x=2 //Error: Assignment to constant variable

score 11 · Accepted Answer · answered Dec 11 '18 at 11:39

11

That's an effect of the immutable exported module values. You can override that with another function in the same module

In your file 1 :

export let x = 1;
export function modifyX( value ) { x = value; }

In your file 2

import { x, modifyX } from "file1.js"

console.log( x ) // 1;
modifyX( 2 );
console.log( x ) // 2;

answered Dec 11 '18 at 11:39

drinchev

and yet we can assign properties directly to x. x.foo = 2; works fine, if we have export let x = { foo: 3 }; So the value isn't immutable. Only the binding to the top level value. – a101010 Apr 20 '23 at 01:17

score 0 · Answer 2 · answered May 22 '22 at 11:21

you can try to set the x as an object property like this:

export default {
    x: 1
}

then from your second file:

import file1API from "./file1.js";

console.log(file1API.x); //1
file1API.x = 2;
console.log(file1API.x); //2

note that the value of x will also be updated in "file1.js".

2 Answers2