How to get sequence number in map function in JavaScript?

Question

Is there a way for me to get the sequence number of each item in a map function in JavaScript?

For example, I have an array of 5 items and would like to pass the sequence number of each item to my React component in the following code:

{toDoList.map(item => <ToDoItem key={item.id} sequenceNumber={???} data={item} />)}

Answer 1

the three parameters to callback function inside map are element, index and array itself, so you only need to give a second argument to callback function like:

var arr = [1,2,3,4];

arr.map((num, index) => console.log(num + " " + index));

so in your case it will be:

{toDoList.map((item, index) => <ToDoItem key={item.id} sequenceNumber={index} data={item} />)}