no-plusplus - Eslint

Because the unary ++ and -- operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code.

let i = 10;
let j = 20;

i ++
j
// i = 11, j = 20

let i = 10;
let j = 20;

i
++
j
// i = 10, j = 21

Rule Details

This rule disallows the unary operators ++ and --.

Examples of incorrect code for this rule:

::: incorrect

/*eslint no-plusplus: "error"*/

let foo = 0;
foo++;

let bar = 42;
bar--;

for (let i = 0; i < l; i++) {
    doSomething(i);
}

:::

Examples of correct code for this rule:

::: correct

/*eslint no-plusplus: "error"*/

let foo = 0;
foo += 1;

let bar = 42;
bar -= 1;

for (let i = 0; i < l; i += 1) {
    doSomething(i);
}

:::

Options

This rule has an object option.

"allowForLoopAfterthoughts": true allows unary operators ++ and -- in the afterthought (final expression) of a for loop.

allowForLoopAfterthoughts

Examples of correct code for this rule with the { "allowForLoopAfterthoughts": true } option:

::: correct

/*eslint no-plusplus: ["error", { "allowForLoopAfterthoughts": true }]*/

for (let i = 0; i < l; i++) {
    doSomething(i);
}

for (let i = l; i >= 0; i--) {
    doSomething(i);
}

for (let i = 0, j = l; i < l; i++, j--) {
    doSomething(i, j);
}

:::

Examples of incorrect code for this rule with the { "allowForLoopAfterthoughts": true } option:

::: incorrect

/*eslint no-plusplus: ["error", { "allowForLoopAfterthoughts": true }]*/

for (let i = 0; i < l; j = i++) {
    doSomething(i, j);
}

for (let i = l; i--;) {
    doSomething(i);
}

for (let i = 0; i < l;) i++;

:::