assign.md

Assign a Property after from()

If we create an object by the method .from():

const A = shape({
  foo: {
    validate: v => v > 10
  }
})

const a = A.from({
  foo: 11
})

And the validator has been transplanted into the setter of the property foo.

If we assign a wrong value to foo, there will be an error.

a.foo = 5
// throw Error
// - code: VALIDATION_FAILS
// - ...

If we assign a right value:

a.foo = 20
console.log(a.foo)  // prints 20

Async Setter

But if the object is generated by an async skema, we can't just assign the value with the = operator, we have to use the set method to make it asynchronously due to the limitation of the JavaScript programming language.

The statement of = operator always returns the value to be assigned instantly, but not the return value of the setter function.

const {shape, set} from 'skema'
const B = shape({
  foo: {
    set (v) {
      return new Promise((resolve) => {
        setTimeout(() => {
          resolve(v + 1)
        }, 10)
      })
    }
  }
})

async function run () {
  const b = await B.from({
    foo: 1
  })

  console.log(b.foo)  // 2

  const result = await set(b, 'foo', 10)
  console.log(b.foo, result)  // 11 11
}

run()