eslint: [no-unused-vars] is not reported in a scenario.

I am using eslint@2.8.0 babel-eslint@6.0.4 node v6.0.0 npm 3.8.6

My rule is set to "no-unused-vars": 1

function test(options) {
    options = options || {};
    // Shouldn't this should give no-unused-vars error here?
}

test({});

In above scenario since options object is not used thus IMHO this should raise no-unused-vars error.

I tested this on online demo of eslint also.

About this issue

Original URL
State: closed
Created 8 years ago
Comments: 16 (12 by maintainers)

Commits related to this issue

Update: `no-unused-vars` ignores read it modifies itself (fixes #6348) `no-unused-vars` comes to ignore a read of a modification of itself. - A read in RHS of an assignment to itself (e.g. `a = a + ... — committed to eslint/eslint by mysticatea 8 years ago
Update: `no-unused-vars` ignores read it modifies itself (fixes #6348) `no-unused-vars` comes to ignore a read of a modification of itself. - A read in RHS of an assignment to itself (e.g. `a = a + ... — committed to eslint/eslint by mysticatea 8 years ago
Update: `no-unused-vars` ignores read it modifies itself (fixes #6348) (#6535) * Update: `no-unused-vars` ignores read it modifies itself (fixes #6348) `no-unused-vars` comes to ignore a read of a... — committed to eslint/eslint by mysticatea 8 years ago

Most upvoted comments

Hmm… I’ve reconsidered. I think it might be sufficient to provide an option which simply says, if a variable is on LHS and RHS of an assignment, don’t assume it is used.

function myFunc(a) {
    a = a + 1;
    // But wait, I'm still not really using a beyond the assignment,
    // so the assignment was actually pretty useless.
}

Also, I’m wondering about the compound-assignment operators. Do they count as usage?

function myOtherFunc(a) {
    a += 1;  // Is this a "use" per no-unused-params?
}

If the compound-assignment doesn’t count as a use, I fail to see how unwrapped assign-after-operator (a = a + 1) should count as a use either.

platinumazure on Jun 9, 2016

👍 for @platinumazure’s suggestion, not optional. That is, until a is used for something other than self assignment, consider it unused.

mikesherov on Jun 21, 2016

imo this exception should only cover assignment if the RHS is a combination of LHS, a literal, and shortcircuiting operators.

Note that the snippet

function test(count) {
    count = count + 1;
}

test({
    value: 1,
    toString() {
        console.log(`called (${this.value})`);
        return String(this.value++);
    }
});

does use the argument

Slayer95 on Jun 9, 2016

@vitorbal I think a good check is to see if the same variable is on both left and right side of the assignment expression. In that case, it should not be considered as “use”.

ilyavolodin on Jun 9, 2016