ESLint throws an error when trying to assign multiple variables to the same value

问题

Why does ESLint throw a Parsing error: Unexpected token , after a variable declaration on this line of code?

const a, b, c = 1;

My .eslintrc.json looks like this;

{

    "env": {
        "browser": true,
        "es6": true,
        "jquery": true,
        "commonjs": true
    },
    "extends": [
        "airbnb-base",
        "prettier"
    ],
    "parserOptions": {
        "ecmaVersion": 6,
        "sourceType": "script"
    },
    "plugins": ["prettier"],
    "rules": {
        "prettier/prettier": "error",
        "semi": ["error", "always"],
        "quotes": ["error", "double"]
    }

}

回答1:

You cannot do that in JS.

If multiple variables listed in a variable declaration (either var, let or const), each value has its own initializer, so it's impossible to assign a single value to multiple variables in a single declaration statement, without repetition.

If an initializer is missing (no = value part present), the variable will be set to undefined.

So if you used let, then c would become 1, while a and b would be undefined:

let a, b, c = 1;

console.log(a, b, c) //undefined undefined 1

However, omitting the initializer in a const declaration throws an error (it doesn't make too much sense to assign undefined to a constant, right?)

Therefore, your code fails (not just in ESLint, but in any JS runtime that correctly implements the ECMAScript standard):

const a, b, c = 1; //SyntaxError

To assign the same value to multiple variables, you have to either:

Repeat the value (this won't work if the value is an object literal (including array literals and function expressions) or returned by a constructor, a factory, or non-pure function):
```
const a = 1, b = 1, c = 1;

console.log(a, b, c) //1 1 1
```
Assign the variables from each other (tip: put the one with the shortest name first and repeat that one):
```
const a = 1, b = a, c = a;

console.log(a, b, c) //1 1 1
```

Use let:

let a, b, c;
a = b = c = 1

console.log(a, b, c) //1 1 1

Destructure an infinite iterator (that seems useful in case of a very large number of variables):

const [a, b, c] = (function*(v){while(true) yield v})(1);
                                                   // ^--- Value

console.log(a, b, c) //1 1 1

来源：https://stackoverflow.com/questions/62090461/eslint-throws-an-error-when-trying-to-assign-multiple-variables-to-the-same-valu

标签

javascript

eslint