no-unused-expressions : sequence expressions

Tell us about your environment

• ESLint Version: v3.15.0
• Node Version: v7.3.0
• npm Version: v3.10.8

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

Please show your full configuration: .eslintrc.js

module.exports = {
    root: true,
    parserOptions: {
        ecmaVersion: 8,
    },
    rules: {
        'no-unused-expressions': [2, { 'allowShortCircuit': true, 'allowTernary': true }]
    }
};

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

let readFile = function (filePath, encoding, cb) {
    if (typeof encoding === 'function')
      cb = encoding, encoding = 'utf8';
    // ...
    return [encoding, cb];
};

What did you expect to happen? As the rule name says “no unused expressions”, I wouldn’t expect an error for the example above.

There is an example in the docs: c = a, b; This is obviously an unused expression and the rule should error in this case. But I can’t see something unused in this one: cb = encoding, encoding = ‘utf8’; It’s just 2 AssignmentExpression inside of a SequenceExpression. So, I am wondering if I’m right and this rule can be changed slightly.

What actually happened? Please include the actual, raw output from ESLint. $ eslint ./test.js > output.txt

C:\nodejs\test\test.js
  3:7  error  Expected an assignment or function call and instead saw an expression  no-unused-expressions

✖ 1 problem (1 error, 0 warnings)

[platinumazure]

It’s true that expression isn’t technically useless, but it is confusing to read and there exists a more conventional equivalent:

cb = encoding;
encoding = "utf8";

[ilyavolodin]

I’m going to lock this thread. This is not a right venue for this type of conversation.

P.S. @nemoxps You are having a discussion about knowledge of JS with one of the members of TC39. I don’ t think the argument is on your side.