typescript/strict-boolean-expressions Pedantic ​
What it does ​
Disallow certain types in boolean expressions.
Why is this bad? ​
Forbids usage of non-boolean types in expressions where a boolean is expected. boolean and never types are always allowed. Additional types which are considered safe in a boolean context can be configured via options.
The following nodes are checked:
- Arguments to the
!,&&, and||operators - The condition in a conditional expression (
cond ? x : y) - Conditions for
if,for,while, anddo-whilestatements.
Examples ​
Examples of incorrect code for this rule:
ts
const str = "hello";
if (str) {
console.log("string");
}
const num = 42;
if (num) {
console.log("number");
}
const obj = { foo: "bar" };
if (obj) {
console.log("object");
}
declare const maybeString: string | undefined;
if (maybeString) {
console.log(maybeString);
}
const result = str && num;
const ternary = str ? "yes" : "no";Examples of correct code for this rule:
ts
const str = "hello";
if (str !== "") {
console.log("string");
}
const num = 42;
if (num !== 0) {
console.log("number");
}
const obj = { foo: "bar" };
if (obj !== null) {
console.log("object");
}
declare const maybeString: string | undefined;
if (maybeString !== undefined) {
console.log(maybeString);
}
const bool = true;
if (bool) {
console.log("boolean");
}Configuration ​
This rule accepts a configuration object with the following properties:
allowAny ​
type: boolean
default: false
Whether to allow any type in boolean contexts.
allowNullableBoolean ​
type: boolean
default: false
Whether to allow nullable boolean types (e.g., boolean | null) in boolean contexts.
allowNullableEnum ​
type: boolean
default: false
Whether to allow nullable enum types in boolean contexts.
allowNullableNumber ​
type: boolean
default: false
Whether to allow nullable number types (e.g., number | null) in boolean contexts.
allowNullableObject ​
type: boolean
default: true
Whether to allow nullable object types in boolean contexts.
allowNullableString ​
type: boolean
default: false
Whether to allow nullable string types (e.g., string | null) in boolean contexts.
allowNumber ​
type: boolean
default: true
Whether to allow number types in boolean contexts (checks for non-zero numbers).
allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing ​
type: boolean
default: false
Whether to allow this rule to run without strictNullChecks enabled. This is not recommended as the rule may produce incorrect results.
allowString ​
type: boolean
default: true
Whether to allow string types in boolean contexts (checks for non-empty strings).
How to use ​
To enable this rule in the CLI or using the config file, you can use:
bash
oxlint --type-aware --deny typescript/strict-boolean-expressionsjson
{
"rules": {
"typescript/strict-boolean-expressions": "error"
}
}