New JavaScript syntax “double question mark syntax” and “optional chain syntax”

Time:2021-2-27

Double question mark grammar

Double question mark grammar
The concept is to return the value on the right when the value on the left is null or undefined

let Form = undefined ?? true;   //Form = true

Alternative chain syntax

? optional chain

//Optional chain
let body = {
    value: {
        a: '123321'
    }
}
let flag = body ? body.value : undefined
//Equivalent to
let result = body?.value
console.log(result);

//Actual
let select = {
    value: {
        a: null
    }
}
let entirely = select?.value?.a || 100
//If select and select.value and select.value When. A are null or undefined, the entity is equal to 100
console.log(entirely)
//If a = 0, entity must be equal to 100, which can only be written as follows

let over = select.value.a === null ? 100 : select?.value?.a

The code is stored in GitHub

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