JavaScript functions can be written as a FunctionDeclaration function foo() { ... } or as a FunctionExpression const foo = function() { ... };. While a JavaScript interpreter might tolerate it, overwriting/reassigning a function written as a FunctionDeclaration is often indicative of a mistake or issue.

function foo() {}
foo = bar;

Rule Details

This rule disallows reassigning function declarations.

Examples of incorrect code for this rule:

::: incorrect

/*eslint no-func-assign: "error"*/

function foo() {}
foo = bar;

function baz() {
    baz = bar;
}

let a = function hello() {
  hello = 123;
};

:::

Examples of incorrect code for this rule, unlike the corresponding rule in JSHint:

::: incorrect

/*eslint no-func-assign: "error"*/

foo = bar;
function foo() {}

:::

Examples of correct code for this rule:

::: correct

/*eslint no-func-assign: "error"*/

let foo = function () {}
foo = bar;

function baz(baz) { // `baz` is shadowed.
    baz = bar;
}

function qux() {
    const qux = bar;  // `qux` is shadowed.
}

:::