# E0286: lower case letters compared with toUpperCase

Comparing the result of a function named `toUpperCase` to a string literal with one or more lower case letters will always yield the same result.

    let x = "BaNaNa";

    // always returns 'false'
    if (x.toUpperCase() === "banana") {
    }

    // always returns 'true'
    if (x.toUpperCase() !== "banana") {
    }

Introduced in quick-lint-js version 2.9.0.

Documentation for other errors