在javascript中使用条件编写扩展运算符的更好方法

Question

I'm looking for a better way to write the following code:

let fromCreatedAt;
let toCreatedAt = new Date();

const someObject = {
    ...((!!fromCreatedAt || !!toCreatedAt) ? {
        createdAt: {
            ...(!!fromCreatedAt ? {
                from: fromCreatedAt,
            } : {}),
            ...(!!toCreatedAt ? {
                to: toCreatedAt,
            } : {}),
        },
    } : {}),
}

console.log(someObject); // { createdAt: { to: 2020-11-18T05:32:57.697Z } }

fromCreatedAt and toCreatedAt are variables that can change and generate a different object.

This is just an example, but you could have an object that repeats the conditions of the createdAt field multiple times for other fields, so you would find a way to refactor that repeated functionality.

Answer 1

I'd use shorthand properties to create the createdAt nested object, removing undefined values by filtering through Object.fromEntries . Then you can create the someObject depending on whether the createdAt object has any keys or not:

 let from; let to = new Date(); const createdAt = Object.fromEntries( Object.entries({ from, to }).filter(([, val]) => val !== undefined) ); const someObject = Object.keys(createdAt).length ? { createdAt } : {}; console.log(someObject);

Answer 2

You could create objects using shorthand property name and conditionally spread it

 let fromCreatedAt, toCreatedAt = new Date(), from = fromCreatedAt, to = toCreatedAt; const createdAt = { ...(from && { from }), ...(to && { to }) }, someObject = { ...(from || to && { createdAt }) } console.log(someObject)

Answer 3

Because ...null and ...undefined will cause no data properties to be copied, you could get rid of the ternary operators and simplify to boolean short-circuit evaluation:

 let fromCreatedAt; let toCreatedAt = new Date(); const someObject = { ...(fromCreatedAt || toCreatedAt) && { createdAt: { ...fromCreatedAt && { from: fromCreatedAt}, ...toCreatedAt && { to: toCreatedAt}, } } }; console.log(someObject);

I thought this might be a little more elegant, but it doesn't get rid of the duplicate conditions, so probably doesn't answer the question completely.