CODEWITHSUNDEEP
javascriptreactjs
Relaxing White Rain Music
Relaxing White Rain Music

Reputation: 1

Null check for mapping an array in react

{data?.map((item, index) =>

How does the above line of code check for an empty array before mapping? I am not seeing any references for such. Any body please explain?

what does data? do?

Reference here: https://dev.to/madara/fetching-data-with-react-hooks-and-fetch-api-beginners-guide-2ick

Upvotes: 0

Views: 3893

Answers (2)

Noor Ul Ain
Noor Ul Ain

Reputation: 600

Adding ternary operator after data (data?) would check first that the data has a value and is not null or undefined, so it can not throw error in that case. It's a short hand for:

data ? data.map((item, index) => {}) : null

If the data has a value, it would execute map on it.

Upvotes: 0

Salah ED
Salah ED

Reputation: 635

This is a condition, it check if the data exists befor map to avoid returning the error message "data is null" or "data is undefined".

data?.map((item, index) => { ... })

is the same as

data 
? data.map((item, index) => { ... }) 
: null

and the same as

if (data) 
data.map((item, index) => { ... })

Upvotes: 1

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