Destructuring two variables and reassigning the value of one is hard with let and const

[ericandrewlewis]

Tell us about your environment

• ESLint Version: 3.16.1
• Node Version: v6.6.0
• npm Version: 3.10.3

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

module.exports = {
  "env": {
    "browser": true,
    "es6": true
  },
  "extends": "eslint:recommended",
  "parserOptions": {
    "sourceType": "module",
    "ecmaFeatures": {
      "experimentalObjectRestSpread": true
    }
  },
  "rules": {
    "prefer-const": ["error", {
      "destructuring": "any",
      "ignoreReadBeforeAssign": false
    }],
    "no-console": "off"
  }
};

What did you do? Please include the actual source code causing the issue.

I have a basic test case of the problem in this code:

const props = {
  name: "Eric",
  age: 30,
  occupation: "Artist"
}

let { name, age } = props;
age = 3;

console.log(name);
console.log(age);

ESLint says that let { name, age } = props; is a problem and should use const.

Here, two variables are created via destructuring syntax, and one is later reassigned but the other is not.

Fixing the code as the rule suggests means using const, which creates a syntax error.

What did you expect to happen?

I'm not sure :)

What actually happened? Please include the actual, raw output from ESLint.

$ ./node_modules/.bin/eslint app.js

/Users/eric/Desktop/eslint/app.js
  7:7  error  'name' is never reassigned. Use 'const' instead  prefer-const

✖ 1 problem (1 error, 0 warnings)

[ljharb]

The proper way to fix this is:

const { name } = props;
let { age } = props;

[not-an-aardvark]

Does the destructuring: "all" option solve your issue?

[ericandrewlewis]

Sorry, I made an over-simplified example that missed my problem.

In the case of using a rest operator, where you want to get an object that is only some properties of an object.

const props = {
  name: "Eric",
  age: 30,
  occupation: "Artist"
}

let { name, ...otherProps } = props;
otherProps = 3;

console.log(name);
console.log(otherProps);

I just tried destructuring: "all" with this example but I still get the error.

[vitorbal]

@ericandrewlewis apologies for the delay. Thank you for clarifying your example. I tried it locally and it does indeed report an error, even with the destructuring: "all" option set. I believe this is a bug. I'll work on this.

[ericandrewlewis]

🎊