JavaScript Objects

Destructure 3 levels down

match = obj?.props?.match;

If you know the property will exist

const {
    props: { match },
} = obj;

const {
    a: {
        b: { c },
    },
} = obj;

Default Dict

(obj['key'] || obj['key'] = []).push('value')

(obj['key'] || obj['key'] = 0) += 1

new keyword

1. Creates a new object 2. type: object
2. It sets this new object's internal, inaccessible, [[prototype]] (proto) property to be the constructor function's external, accessible, prototype object (every function object automatically has a prototype property).
3. Variable points to the newly created object.
4. Executes the constructor function
5. Return the new object
   1. unless the constructor function returns a non-null object reference.
   2. In this case, that object reference is returned instead.

How do you know if they used new?

function Foo() {
    if (!new.target) {
        throw "Foo() must be called with new";
    }
}

Why Set() returns an error without new

• without the new, the constructor will get called as a regular function
• it will use this from the caller's context and not from Set and it might break

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Last update: 2023-04-24