no-use-before-define
Disallow the use of variables before they are defined.
Examples
This rule extends the base eslint/no-use-before-define
rule.
It adds support for type
, interface
and enum
declarations.
How to Use
module.exports = {
"rules": {
// Note: you must disable the base rule as it can report incorrect errors
"no-use-before-define": "off",
"@typescript-eslint/no-use-before-define": "warn"
}
};
Options
See eslint/no-use-before-define
options.
This rule adds the following options:
interface Options extends BaseNoUseBeforeDefineOptions {
enums?: boolean;
typedefs?: boolean;
ignoreTypeReferences?: boolean;
}
const defaultOptions: Options = {
...baseNoUseBeforeDefineDefaultOptions,
enums: true,
typedefs: true,
ignoreTypeReferences: true,
};
enums
If this is true
, this rule warns every reference to a enum before the enum declaration.
If this is false
, this rule will ignore references to enums, when the reference is in a child scope.
Examples of code for the { "enums": true }
option:
- ❌ Incorrect
- ✅ Correct
/*eslint no-use-before-define: ["error", { "enums": true }]*/
const x = Foo.FOO;
enum Foo {
FOO,
}
/*eslint no-use-before-define: ["error", { "enums": false }]*/
function foo() {
return Foo.FOO;
}
enum Foo {
FOO,
}
typedefs
If this is true
, this rule warns every reference to a type before the type declaration.
If this is false
, this rule will ignore references to types.
Examples of correct code for the { "typedefs": false }
option:
/*eslint no-use-before-define: ["error", { "typedefs": false }]*/
let myVar: StringOrNumber;
type StringOrNumber = string | number;
ignoreTypeReferences
If this is true
, this rule ignores all type references, such as in type annotations and assertions.
If this is false
, this will will check all type references.
Examples of correct code for the { "ignoreTypeReferences": true }
option:
/*eslint no-use-before-define: ["error", { "ignoreTypeReferences": true }]*/
let var1: StringOrNumber;
type StringOrNumber = string | number;
let var2: Enum;
enum Enum {}
Resources
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