noStringCaseMismatch (since v11.0.0)
Disallow comparison of expressions modifying the string case with non-compliant value.
Examples
Invalid
if (s.toUpperCase() === "Abc") {}nursery/noStringCaseMismatch.js:1:5 lint/nursery/noStringCaseMismatch FIXABLE ━━━━━━━━━━━━━━━━━━━━
✖ This expression always returns false.
> 1 │ if (s.toUpperCase() === "Abc") {}
│ ^^^^^^^^^^^^^^^^^^^^^^^^^
2 │
ℹ This call convert the string to upper case
> 1 │ if (s.toUpperCase() === "Abc") {}
│ ^^^^^^^^^^^^^^^
2 │
ℹ ... but this value is not in upper case
> 1 │ if (s.toUpperCase() === "Abc") {}
│ ^^^^^
2 │
ℹ Suggested fix: Use upper case string value.
1 │ - if·(s.toUpperCase()·===·"Abc")·{}
1 │ + if·(s.toUpperCase()·===·"ABC")·{}
2 2 │
while (s.toLowerCase() === "Abc") {}nursery/noStringCaseMismatch.js:1:8 lint/nursery/noStringCaseMismatch FIXABLE ━━━━━━━━━━━━━━━━━━━━
✖ This expression always returns false.
> 1 │ while (s.toLowerCase() === "Abc") {}
│ ^^^^^^^^^^^^^^^^^^^^^^^^^
2 │
ℹ This call convert the string to lower case
> 1 │ while (s.toLowerCase() === "Abc") {}
│ ^^^^^^^^^^^^^^^
2 │
ℹ ... but this value is not in lower case
> 1 │ while (s.toLowerCase() === "Abc") {}
│ ^^^^^
2 │
ℹ Suggested fix: Use lower case string value.
1 │ - while·(s.toLowerCase()·===·"Abc")·{}
1 │ + while·(s.toLowerCase()·===·"abc")·{}
2 2 │
Valid
if (s.toUpperCase() === "ABC") {}
while (s.toLowerCase() === "abc") {}
for (;s.toLocaleLowerCase() === "ABC";) {}
while (s.toLocaleUpperCase() === "abc") {}
for (let s = "abc"; s === "abc"; s = s.toUpperCase()) {}