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

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?

CodePudding user response：

You can only change a function expression and not a function declaration. If you store a function expression in a variable and return it from an exported function then you can change it.

const noop = () => {}

const firstMouseUp = () => {
}

let func = firstMouseUp;

export function getFunc () {
  return func;
}

export function removeFirstMouseUp() {
  func = noop;
}

Play here

CodePudding user response：

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.

CodePudding user response：

It would seem you are just looking for

export function noop() {}

export function removeFirstMouseUp() {
  return(noop);
}