How to add properties in object conditionally
When building an object in JavaScript or TypeScript, it's common to add properties conditionally, based on the evaluation of expressions. This is typically done using the spread operator (...) in combination with logical conditions.
const condition = (a, b) → a › b; const obj = {
a: 1, b: 2,
... (false && {c: 3}),
... (true && {d: 4}),
... (condition (1, 2) && {e: 5}),
};
console.log(obj); // output: { a: 1, b: 2, d: 4 }
Explanation
false && {c: 3}
: This evaluates tofalse
, meaning the{c: 3}
object is not spread into obj.true && {d: 4}
: Since the condition is true,{d: 4}
is spread into obj.condition(1, 2) && {e: 5}
: The condition function evaluates whether a > b. Since 1 > 2 is false, the object{e: 5}
is not spread.
This technique is a powerful way to keep your object definition clean and concise while adding properties dynamically based on various conditions.
Output
The final object looks like this:
{ a: 1, b: 2, d: 4 }
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