| title | rule_type | further_reading |
|---|---|---|
valid-typeof |
problem |
For a vast majority of use cases, the result of the typeof operator is one of the following string literals: "undefined", "object", "boolean", "number", "string", "function", "symbol", and "bigint". It is usually a typing mistake to compare the result of a typeof operator to other string literals.
This rule enforces comparing typeof expressions to valid string literals.
Examples of incorrect code for this rule:
::: incorrect
/*eslint valid-typeof: "error"*/
typeof foo === "strnig"
typeof foo == "undefimed"
typeof bar != "nunber"
typeof bar !== "fucntion":::
Examples of correct code for this rule:
::: correct
/*eslint valid-typeof: "error"*/
typeof foo === "string"
typeof bar == "undefined"
typeof foo === baz
typeof bar === typeof qux:::
This rule has an object option:
"requireStringLiterals": trueallows the comparison oftypeofexpressions with only string literals or othertypeofexpressions, and disallows comparisons to any other value. Default isfalse.
Examples of incorrect code with the { "requireStringLiterals": true } option:
::: incorrect
/*eslint valid-typeof: ["error", { "requireStringLiterals": true }]*/
typeof foo === undefined
typeof bar == Object
typeof baz === "strnig"
typeof qux === "some invalid type"
typeof baz === anotherVariable
typeof foo == 5:::
Examples of correct code with the { "requireStringLiterals": true } option:
::: correct
/*eslint valid-typeof: ["error", { "requireStringLiterals": true }]*/
typeof foo === "undefined"
typeof bar == "object"
typeof baz === "string"
typeof bar === typeof qux:::
You may want to turn this rule off if you will be using the typeof operator on host objects.