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# Disallow mixes of different operators (no-mixed-operators) | ||
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Enclosing complex expressions by parentheses clarifies the developer's intention, which makes the code more readable. | ||
This rule warns when different operators are used consecutively without parentheses in an expression. | ||
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```js | ||
var foo = a && b || c || d; /*BAD: Unexpected mix of '&&' and '||'.*/ | ||
var foo = (a && b) || c || d; /*GOOD*/ | ||
var foo = a && (b || c || d); /*GOOD*/ | ||
``` | ||
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## Rule Details | ||
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This rule checks `BinaryExpression` and `LogicalExpression`. | ||
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This rule may conflict with [no-extra-parens] rule. | ||
If you use both this and [no-extra-parens] rule together, you need to use the `nestedBinaryExpressions` option of [no-extra-parens] rule. | ||
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Examples of **incorrect** code for this rule: | ||
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```js | ||
/*eslint no-mixed-operators: "error"*/ | ||
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var foo = a && b < 0 || c > 0 || d + 1 === 0; | ||
var foo = a + b * c; | ||
``` | ||
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Examples of **correct** code for this rule: | ||
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```js | ||
/*eslint no-mixed-operators: "error"*/ | ||
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var foo = a || b || c; | ||
var foo = a && b && c; | ||
var foo = (a && b < 0) || c > 0 || d + 1 === 0; | ||
var foo = a && (b < 0 || c > 0 || d + 1 === 0); | ||
var foo = a + (b * c); | ||
var foo = (a + b) * c; | ||
``` | ||
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## Options | ||
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```json | ||
{ | ||
"no-mixed-operators": [ | ||
"error", | ||
{ | ||
"groups": [ | ||
["+", "-", "*", "/", "%", "**"], | ||
["&", "|", "^", "~", "<<", ">>", ">>>"], | ||
["==", "!=", "===", "!==", ">", ">=", "<", "<="], | ||
["&&", "||"], | ||
["in", "instanceof"] | ||
], | ||
"allowSamePrecedence": true | ||
} | ||
] | ||
} | ||
``` | ||
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This rule has 2 options. | ||
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* `groups` (`string[][]`) - specifies groups to compare operators. | ||
When this rule compares two operators, if both operators are included in a same group, this rule checks it. Otherwise, this rule ignores it. | ||
This value is a list of groups. The group is a list of binary operators. | ||
Default is the groups for each kind of operators. | ||
* `allowSamePrecedence` (`boolean`) - specifies to allow mix of 2 operators if those have the same precedence. Default is `true`. | ||
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### groups | ||
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The following operators can be used in `groups` option: | ||
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* Arithmetic Operators: `"+"`, `"-"`, `"*"`, `"/"`, `"%"`, `"**"` | ||
* Bitwise Operators: `"&"`, `"|"`, `"^"`, `"~"`, `"<<"`, `">>"`, `">>>"` | ||
* Comparison Operators: `"=="`, `"!="`, `"==="`, `"!=="`, `">"`, `">="`, `"<"`, `"<="` | ||
* Logical Operators: `"&&"`, `"||"` | ||
* Relational Operators: `"in"`, `"instanceof"` | ||
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Now, considers about `{"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}` configure. | ||
This configure has 2 groups: bitwise operators and logical operators. | ||
This rule checks only if both operators are included in a same group. | ||
So, in this case, this rule comes to check between bitwise operators and between logical operators. | ||
This rule ignores other operators. | ||
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Examples of **incorrect** code for this rule with `{"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}` option: | ||
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```js | ||
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/ | ||
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var foo = a && b < 0 || c > 0 || d + 1 === 0; | ||
var foo = a & b | c; | ||
``` | ||
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Examples of **correct** code for this rule with `{"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}` option: | ||
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```js | ||
/*eslint no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/ | ||
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var foo = a || b > 0 || c + 1 === 0; | ||
var foo = a && b > 0 && c + 1 === 0; | ||
var foo = (a && b < 0) || c > 0 || d + 1 === 0; | ||
var foo = a && (b < 0 || c > 0 || d + 1 === 0); | ||
var foo = (a & b) | c; | ||
var foo = a & (b | c); | ||
var foo = a + b * c; | ||
var foo = a + (b * c); | ||
var foo = (a + b) * c; | ||
``` | ||
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### allowSamePrecedence | ||
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Examples of **correct** code for this rule with `{"allowSamePrecedence": true}` option: | ||
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```js | ||
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": true}]*/ | ||
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// + and - have the same precedence. | ||
var foo = a + b - c; | ||
``` | ||
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Examples of **incorrect** code for this rule with `{"allowSamePrecedence": false}` option: | ||
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```js | ||
/*eslint no-mixed-operators: ["error", {"allowSamePrecedence": false}]*/ | ||
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// + and - have the same precedence. | ||
var foo = a + b - c; | ||
``` | ||
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## When Not To Use It | ||
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If you don't want to be notified about mixed operators, then it's safe to disable this rule. | ||
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## Related Rules | ||
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* [no-extra-parens] | ||
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[no-extra-parens]: no-extra-parens.md |
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