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Just getting started with Flow but can't seem to understand what it wants me to do with adding types for destructuring objects like i.e. props
i.e.
render({ count }, { displayHelp }) {
Throws an error like
16: render({ count }, { displayHelp }) {
^^^^^^^^^ destructuring. Missing annotation
and when I add annotation it still complains
17: render({ count: number }, { displayHelp }) {
^^^^^^^^^^^^^^^^^ destructuring. Missing annotation
I am obviously missing something very simple here if anybody could point out ?
303
How to avoid repetition and keep your code clean with destructuring assignment in React Destructuring assignment is a feature of JavaScript introduced by ES6 (or ES 2015) that’s available for both object and array data types.
When destructuring arrays, the order that variables are declared is important. If we only want the car and suv we can simply leave out the truck but keep the comma: Destructuring comes in handy when a function returns an array: Get Certified! Complete the React modules, do the exercises, take the exam and become w3schools certified!!
In fact, the useState hook from React returns an array with two values that we destructure immediately. Here’s an illustration of how it works: The benefits of using destructuring assignment is especially visible when using React because you would deal with state and props frequently.
First, destructure the userData props before passing it to the component: Then pass it into the component as two props: Or you can also use spread operator so you don’t need to destructure it: Then immediately destructure the props object when you define the parameters in the function, like this:
The problem with doing { count: number } is that this clashes with ES6 syntax for destructuring assignment, where you can use { a: b } = c in order to take the value with key a from c and have it be named b, ie:
const c = { a: 1 }
const { a: b } = c
//b is now a constant with value 1
There isn't really a good workaround for this in Flow right now, but this seems to work (although it is ugly):
render({...}: { count: number }, { displayHelp }) {
The best way right now seems to be to create a custom type which captures your props:
type propsForThisComponent = {
propA: someType
propB: anotherType
...
}
and then do:
render(props: propsForThisComponent) {
This typechecks, although it forces you to access all your props as props.propName.
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