is it possible to assign a function to another function in typescript

February 4, 2022

I want to set current function to null loop in typescript, this is my code looks like:

export function noop() {}

export function removeFirstMouseUp() {
  removeFirstMouseUp = noop;
}

but the compiler told me this error:

 TS2630: Cannot assign to 'removeFirstMouseUp' because it is a function.

assign a function to another function, it seems no problem. why the typescript compiler shows this error? what did I do to fix this problem?

>Solution :

Instead of defining removeFirstMouseUp as a function declaration, rewrite it as a function definition:

export function noop() {}

export let removeFirstMouseUp = function() {
    removeFirstMouseUp = noop;
}

From ESLint’s no-func-assign page:

JavaScript functions can be written as a FunctionDeclaration function foo() { … } or as a FunctionExpression var 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.

ESLint and TypeScript are different, however, in this case the error messages are referring to the same thing.