no-plusplus

Disallow the unary operators ++ and --

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 
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let i = 10; let j = 20; i ++ j // i = 10, j = 21 
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Rule Details

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

Examples of incorrect code for this rule:

/*eslint no-plusplus: "error"*/ let foo = 0; foo++; let bar = 42; bar--; for (let i = 0; i < l; i++) { doSomething(i); } 
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Examples of correct code for this rule:

/*eslint no-plusplus: "error"*/ let foo = 0; foo += 1; let bar = 42; bar -= 1; for (let i = 0; i < l; i += 1) { doSomething(i); } 
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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:

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

/*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++; 
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Version

This rule was introduced in ESLint v0.0.9.

Resources

• Rule source
• Tests source