Why use '{' and '}' to define a javascript variable [duplicate] - javascript

This question already has answers here:
Javascript object bracket notation ({ Navigation } =) on left side of assign
(5 answers)
What does this symbol mean in JavaScript?
(1 answer)
Closed 4 years ago.
I can't seem to find anything in the documentation to understand why the { and } characters are wrapped around variables on some examples I've seen. Can anyone example why we would do that?
For example:
const {app} = require('./app/app.js');

Related

In JavaScript what is this method called where you might define a variable or property as such variable_name$ref [duplicate]

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Rules for unquoted JavaScript Object Literal Keys?
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What characters are valid for JavaScript variable names?
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Closed 1 year ago.
I am seeing it crop up more and more in code I am going through on a new project (can't share due to contractual reasons) where Ill see something like:
{
prop1: value$ref,
$prop2: null
}
I have see ${prop3} before, but never an example without the brackets. Can anyone provide direction as to what the method is, or the operator is or whatever the case?

What is this Javascrip/node variable/constant assinging notation/syntax called ? [duplicate]

This question already has answers here:
What does this symbol mean in JavaScript?
(1 answer)
Javascript object bracket notation ({ Navigation } =) on left side of assign
(5 answers)
Closed 4 years ago.
I've been trying to find out what this notation is called so I can better google it. It's from the gmail api node example but wont run for me.
const {client_secret, client_id, redirect_uris} = credentials.installed;
I think this is the correct stackexchange site for this, but if I'm wrong, happy to relocate it to a more appropriate one.
It is Destructuring Assignment

Can someone break this syntax down for me { [ nameValuePair1[, nameValuePair2[, ...nameValuePairN] ] ] } [duplicate]

This question already has answers here:
What do the brackets around the arguments mean when reading documentation for a method? [duplicate]
(3 answers)
How to interpret function parameters in software and language documentation?
(4 answers)
Closed 4 years ago.
I'm looking through the MDN web docs and have seen this parameters for Object
// Object initialiser or literal
{ [ nameValuePair1[, nameValuePair2[, ...nameValuePairN] ] ] }
However, I'm struggling to understand what I'm actually looking at, I know it's an object literal, but the bracket notation is throwing me

Exclamation mark before an object? [duplicate]

This question already has answers here:
What does "!" operator mean in javascript when it is used with a non-boolean variable?
(5 answers)
What is an exclamation point in JavaScript?
(2 answers)
Closed 5 years ago.
Coming from java, learning angular/typescript: The ! negates booleans or boolean expressions. This is, according to my research, the same in javascript/typescript. But what does the following method do?
isSelected(product: Product): boolean {
if (!product || !this.currentProduct) {
return false;
}
return product.sku === this.currentProduct.sku;
}
What is !product? Product is coming in as a method parameter and then it is asked, if product is not product, or wtf should that mean? :D

Can I generate new array with another variable in javascript? [duplicate]

This question already has answers here:
What do square brackets around an expression mean, e.g. `var x = a + [b]`?
(7 answers)
Closed 7 years ago.
function construct(head, tail) {
return cat([head], _.toArray(tail));
}
I'd like to know the role of '[' and ']' above.
Is it an operator?
Is it the array initialize literal?
This question is answered here and on the previous QnA(Use of [square brackets] around JavaScript variables).
I felt this weird because I am not used to javascript.
But this is not a matter any more.
I thought wrong and this is explained. Thanks!
It is initializing a 1 element array to pass to cat here. Brackets can be used to access elements on objects and arrays, and to represent an array literal like you have here.

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