typescript/strict-boolean-expressions Pedantic

💭 This rule requires type information.

🚧 An auto-fix is still under development.

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, and do-while statements.

Examples

Examples of incorrect code for this rule:

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:

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");
}

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --type-aware --deny typescript/strict-boolean-expressions

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/strict-boolean-expressions": "error"
  }
}

References

• Rule Source