++value vs value++
Written byPhuoc Nguyen
Category
JavaScript
Created
15 Jul, 2020
Last updated
22 Aug, 2022
`++`
is the increment operator adding one to the operand.
There're two variables of the operator which use `++`
as prefix or postfix: `++value`
and `value++`
.They have the same effect in for loops. The following loops print the same results which are the numbers from 0 to 4:
for (let i = 0; i < 5; i++) {
console.log(i);
}
// And
for (let i = 0; i < 5; ++i) {
console.log(i);
}
#Differences
When returning a value,
`return value++`
returns the original value before the value is increased. While `return ++value`
increases the value and returns the updated value.The following
`foo`
and `bar`
functions returns different results:const foo = (x) => x++;
const bar = (x) => ++x;
foo(1); // 1
bar(1); // 2
#Good to know
`value += 1`
is another alternative of the postfix increment `value++`
. It's worth noting that they can provide different result when using with strings.The postfix increment
`value++`
will convert the value to number first, and then increase the value:let value = '5';
value++;
value; // 6
On the other hand, if value is a string,
`value += 1`
converts the second argument (`1`
) to string first, and then concatenate them together.let value = '5';
value += 1;
value; // '51'
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Phước Nguyễn