将 1 添加到数组 - Javascript

Question

I just would like to understand why this works:

 let newArray = [0,1,2,3].map(elem => elem + 1); console.log(newArray);

and this doesn't:

 let newArray = [0,1,2,3].map(elem => elem++); console.log(newArray);

Answer 1

That is related to the ++ operator.

return elem++ means return the original value of elem , and after that, elem value will be increased.

To fix this, use ++elem .

Refer to ++ operator .

 let newArray = [0,1,2,3].map(elem => ++elem); console.log(newArray);

Answer 2

if you want return elem after increase you should use ++ operation like this

 let newArray = [0,1,2,3].map(elem => ++elem); console.log(newArray);

Answer 3

it is because you are returning the values before increment. try this

 let newArray = [0,1,2,3].map(elem => ++elem); console.log(newArray);