how to spread an object to a function as arguments?

Question

I have an object an a function which accept arguments, I would like to spread the objects so each property is an argument in that function.

What am I doing wrong in my code?

const args = {
    a: 1
    b: 2
}

const fn = (a, b) => a + b

// i am trying with no success
console.log(fn(...args))

Answer 1

Although the other answers are correct, they change the function signature to accept an object instead of 2 separate arguments. Here is how to use an object's values as function arguments without altering the function's signature. This requires Object.values (ES 2017) and the spread operator to be available in your runtime.

const args = {
  a: 1,
  b: 2
}

const fn = (a, b) => a + b

fn(...Object.values(args));

Keep in mind this will work only in your specific case, since Object.values returns the values of all object keys and doesn't guarantee alphabetical sort order. If you want to take only the values of properties which are named a and b, you can map over Object.keys(args) and filter only those values.

Answer 2

You can use ES6 object destructuring on passed parameter and then just pass your object.

const args = {a: 1, b: 2}

const fn = ({a, b}) => a + b
console.log(fn(args))

You can also set default values for those properties.

const args = {b: 2}

const fn = ({a = 0, b = 0}) => a + b
console.log(fn(args))