打字稿/Javascript：通过字符串名称调用 function

Question

I have a *.ts file with lots of exported functions like:

export function newItemFoo() {
    return {foo: 0, bar: '', baz: true};
}

export function newItemBar() {
    return {foo: 0, bar: ''};
}

export function newItemXXX() {
    return {xxx: 0};
}

I want to make a "magic method" (in the same *.ts ) that can call one of those methods by name, eg:

export function magicMethod(name: string) {
    const newEmptyFunc = new Function(`return new${name}()`);
    return newEmptyFunc();
}
magicMethod('ItemFoo');

but it raise an error

Error: newItemFoo is not defined

It works with eval:

export function magicMethod(name: string) {
    return eval(`newEmpty${name}()`);
}
magicMethod('ItemFoo');

How do I call a function by string name with new Function() ?

Answer 1

Both using eval() and new Function() are convoluted ways to achieve the goal.

Try a simpler approach. Create an object that provides a mapping between the values you want to pass to magicMethod() and the functions to be called. Then implement magicMethod() this way:

function newItemFoo() {
    return {foo: 0, bar: '', baz: true};
}

function newItemBar() {
    return {foo: 0, bar: ''};
}

function newItemXXX() {
    return {xxx: 0};
}

const magicWand: { [K: string]: Function } = {
   Foo: newItemFoo,
   Bar: newItemBar,
   xxx: newItemXXX,   // this allows you to use a different value for the argument
   yyy: newItemXXX,   // ... to use multiple names for the same function
                      // ... and to handle gracefully the calls of non-existing functions 
};

export function magicMethod(name: string) {
  if (magicWand[name]) {
    return magicWand[name]();
  }

  throw new Error(`Method '${name}' is not implemented.`);
}

Usage:

magicMethod('Foo')
// { foo: 0, bar: '', baz: true }
magicMethod('Bar')
// { foo: 0, bar: '' }
magicMethod('xxx')
// { xxx: 0 }
magicMethod('yyy')
// { xxx: 0 }
magicMethod('zzz')
// Error: Method 'zzz' is not implemented.

However, if you provide such a mechanism to invoke the functions defined by the module you probably don't want to make them public using the standard export mechanism but only though magicMethod() . It is the only function that needs to be export -ed.