++value vs value++

++ 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 affect 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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