在 javascript 中编写一个接受任意数量的 object 的 function

Question

I know the implementation of how to pass infinite parameters in a function in javascript.

But how to accepts any number of objects as a parameter in function?

I have this:

function merge<T>(objA:T, objB: T){
  return Object.assign(objA, objB);
}

so that I can do like this:

console.log(`${mergeObject2.age},  ${mergeObject2.name}`);

But how to declare a function if that number of objects is not known..?

for example this:

const mergeObject2 = merge({name: 'Niels'}, {age :39}, {hobby: 'all'});

Thank you.

so if I do it like this:

const mergeObject2 = merge({name: 'Niels'}, {age :39} );

console.log(`${mergeObject2.age},  ${mergeObject2.name}`);

then the output is of course:

39, Niels

But how to do it if you have more objects..?

Answer 1

Fundamentally, if you want to accept N parameters in TypeScript, the varying parameters will all have to have the same type. (It can be a union type, though.) For instance:

function myFunction(a: boolean, b: string, ...rest: Array<number | string>) {
    // ...
}

( Array<number | string> can also be written (number | string)[] .)

That function requires at least two arguments (a boolean and a string ) followed by any number of number or string arguments. Note how the "rest" of the parameters are bundled up in an array, which is why they have to have the same type ( number | string in the example). Of course, once you're dealing with one specific element from that array, you can use if to narrow its type.

If you don't need any fixed parameters ( a and b in the example), just start with the rest parameter.

If you want to use Object.assign in the implementation, you'll need to make the first one required (or hardcode Object.assign 's first argument). So your merge might be:

function merge<T extends object>(target: T, ...sources: T[]): T {
    return Object.assign(target, ...sources);
}
const mergeObject2 = merge({name: "Niels"}, {age: 39}); // ¹
console.log(`${mergeObject2.age},  ${mergeObject2.name}`);

Playground link

That's basically just Object.assign but with the types slightly more restricted (I think), though.

---

¹ You might want to put a {} at the beginning to avoid modifying the {name: "Neils"} object.

Answer 2

You can make use of arguments object available in ES5. It's just like a variable with type array, and is accessible inside a function. It contains the values of all the arguments passed to that function.

function a(){
  let sum = 0;
  for(let i=0;i<arguments.length;i++){
    sum += arguments[i];
  }
  console.log(sum);
}
a(1,2,3);

In your case to copy all objects into one, you can do something like this:

function a(){
  let finalObj = {};
  for(let i=0;i<arguments.length;i++){
    finalObj = {...finalObj,...arguments[i]};
  }
  console.log(finalObj);
}
a({id:1},{name:"sam"},{age: 25});