Avoid variable or function declaration in nested blocks

Docs > Code Analysis > Static Analysis Rules > Avoid variable or function declaration in nested blocks

Metadata

ID: javascript-best-practices/no-inner-declarations

Language: JavaScript

Severity: Warning

Category: Error Prone

Description

Function declarations in JavaScript are generally not block scoped. This rule prevents function declarations inside nested blocks like if statements. Move your declarations to the root of your program, body, or class.

Non-Compliant Code Examples

if (test) { function doSomething() { } }
if (foo) var a;
if (foo) /* some comments */ var a;
if (foo){ function f(){ if(bar){ var a; } } }
if (foo) function f(){ if(bar) var a; }
if (foo) { var fn = function(){} } 
if (foo)  function f(){} 
function bar() { if (foo) var a; }
if (foo){ var a; }
class C { method() { if(test) { var foo; } } }
class C { static { if (test) { function foo() {} } } }
class C { static { if (test) { var foo; } } }
class C { static { if (test) { if (anotherTest) { var foo; } } } }

Compliant Code Examples

function doSomething() { }
function doSomething() { function somethingElse() { } }
(function() { function doSomething() { } }());
function decl() { var fn = function expr() { }; }
function decl(arg) { var fn; if (arg) { fn = function() { }; } }
var x = {doSomething() {function doSomethingElse() {}}}
function decl(arg) { var fn; if (arg) { fn = function expr() { }; } }
function decl(arg) { var fn; if (arg) { fn = function expr() { }; } }
if (test) { let x = 1; }
if (test) { const x = 1; }
function doSomething() { while (test) { var foo; } }
var foo;
var foo = 42;
function doSomething() { var foo; }
(function() { var foo; }());
foo(() => { function bar() { } });
var fn = () => {var foo;}
var x = {doSomething() {var foo;}}
export var foo;
export function bar() {}
export default function baz() {}
exports.foo = () => {}
exports.foo = function(){}
module.exports = function foo(){}
class C { method() { function foo() {} } }
class C { method() { var x; } }
class C { static { function foo() {} } }
class C { static { var x; } }