ES6 import bindings should be immutable

[kzc]

https://2ality.com/2015/07/es6-module-exports.html#es6-modules-export-immutable-bindings

//------ lib.js ------
export let mutableValue = 3;
export function incMutableValue() {
    mutableValue++;
}

//------ main1.js ------
import { mutableValue, incMutableValue } from './lib';

// The imported value is live
console.log(mutableValue); // 3
incMutableValue();
console.log(mutableValue); // 4

// The imported value can’t be changed
mutableValue++; // TypeError in NodeJS, compile error in tsc and rollup

esbuild incorrectly results in no error:

$ esbuild --version
0.5.13

$ esbuild main1.js --bundle | node
3
4

$ echo $?
0

[evanw]

Ah yes, thanks for the reminder. I should make this a compile error. I think this should be pretty straightforward.