Add 1 to array - 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);

"If used postfix, the increment operator increments and returns the value BEFORE incrementing" Increment operator — adiga
– adiga, Commented Jan 19, 2021 at 14:53
developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Andreas
– Andreas, Commented Jan 19, 2021 at 14:54

topdev87 · Accepted Answer · 2021-01-19 15:07:24Z

4

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.

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

answered Jan 19, 2021 at 14:52

topdev87

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Comments

Kimura Shinji · Accepted Answer · 2021-01-19 14:53:35Z

0

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);

answered Jan 19, 2021 at 14:53

Kimura Shinji

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D. Seah · Accepted Answer · 2021-01-19 14:53:51Z

0

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

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

answered Jan 19, 2021 at 14:53

D. Seah

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