What is going on with this assignment? [duplicate] - javascript

This question already has answers here:
Multiple assignment in JavaScript? What does `[ a, b, c ] = [ 1, 2, 3 ]` mean?
(4 answers)
What is destructuring assignment and its uses?
(3 answers)
Closed 2 years ago.
Can someone explain me what is going on here?
const [counter, setCounter] = useState(0);
Is it some kind of assignment?

I think you might need to take a look into the React Hooks docs

It's a destructuring assignment on the results of calling the useState function:
the first element of the array is the value
the second element is a function to change value.

Related

Why are vairable declaration different when we assign the value useState("")? [duplicate]

This question already has answers here:
What does this symbol mean in JavaScript?
(1 answer)
Multiple assignment in JavaScript? What does `[ a, b, c ] = [ 1, 2, 3 ]` mean?
(4 answers)
Closed 9 months ago.
This is what confuses me alot:
When we give a variable a for an example a empty string we do it like this:
const empty = ""
But for useState we do it like this:
const [color, setColor] = useState("Black")
But why? I get so confused that the syntax for useState looks like that.
And ofc searching did not help me.

I want to know the const declaration type of js [duplicate]

This question already has answers here:
Javascript object bracket notation ({ Navigation } =) on left side of assign
(5 answers)
What is destructuring assignment and its uses?
(3 answers)
Closed 3 years ago.
I know how to declare const variable like const a = 1;
but I dont get what is this
const { app, BrowserWindow } = require('electron')
can anyone explain me?
That’s a destructuring assignment.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment
It lets you make shortcuts to members of an array or structure.

Syntax - what does square brackets around a variable declaration mean [duplicate]

This question already has answers here:
Multiple assignment in JavaScript? What does `[ a, b, c ] = [ 1, 2, 3 ]` mean?
(4 answers)
Closed 5 years ago.
Take the following line of code
const [component] = router.getMatchedComponents({ ...to })
Could anyone advise what the square brackets around component means here? I have tried to google this but struggling to find an answer
It's called Destructuring assignment, and it's used to unpack the values of an array and assign them to new variables.
So here in your code:
const [component] = router.getMatchedComponents({ ...to })
You are assigning to the component variable the first element held in the array that will be returned by router.getMatchedComponents({...to}), where to is an array-like structure turned into object using the spread operation.

What is this syntax in JavaScript [duplicate]

This question already has answers here:
Multiple assignment in JavaScript? What does `[ a, b, c ] = [ 1, 2, 3 ]` mean?
(4 answers)
Closed 5 years ago.
Take the following line of code
const [component] = router.getMatchedComponents({ ...to })
Could anyone advise what the square brackets around component means here? I have tried to google this but struggling to find an answer
It's called Destructuring assignment, and it's used to unpack the values of an array and assign them to new variables.
So here in your code:
const [component] = router.getMatchedComponents({ ...to })
You are assigning to the component variable the first element held in the array that will be returned by router.getMatchedComponents({...to}), where to is an array-like structure turned into object using the spread operation.

const keyword usage in Javascript [duplicate]

This question already has answers here:
Javascript object bracket notation ({ Navigation } =) on left side of assign
(5 answers)
ES6 Object Destructuring Default Parameters
(1 answer)
Closed 6 years ago.
I was reading the source for a MeteorJS package (this one) when I came across this:
const {
getMeteorData,
pure = true,
} = expandedOptions;
I did some research to figure out what this code would do, but couldn't find any other instance of const being used like this, or any documentation to clarify it for me.
Any hints, please?
It is using es6 to unpack (or destructure) the values inside the expandedOptions object.
const val = {a:1, b:"hello"};
const {
a,
b
} = val;
console.log(a); //1
console.log(b); //"hello"

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