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@stylistic/js/

no-mixed-operators

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.

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*/

Note: It is expected for this rule to emit one error for each mixed operator in a pair. As a result, for each two consecutive mixed operators used, a distinct error will be displayed, pointing to where the specific operator that breaks the rule is used:

js
var foo = a && b || c || d;

will generate

shell
1:13  Unexpected mix of '&&' and '||'. (no-mixed-operators)
1:18  Unexpected mix of '&&' and '||'. (no-mixed-operators)

Rule Details

This rule checks BinaryExpression, LogicalExpression and ConditionalExpression.

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.

Examples of incorrect code for this rule:

js
/*eslint @stylistic/js/no-mixed-operators: "error"*/

var foo = a 
&&
b < 0
||
c > 0 || d + 1 === 0;
var foo = a
+
b
*
c;
incorrect

Examples of correct code for this rule:

js
/*eslint @stylistic/js/no-mixed-operators: "error"*/

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;
correct

Options

json
{
    "no-mixed-operators": [
        "error",
        {
            "groups": [
                ["+", "-", "*", "/", "%", "**"],
                ["&", "|", "^", "~", "<<", ">>", ">>>"],
                ["==", "!=", "===", "!==", ">", ">=", "<", "<="],
                ["&&", "||"],
                ["in", "instanceof"]
            ],
            "allowSamePrecedence": true
        }
    ]
}

This rule has 2 options.

  • groups (string[][]) - specifies operator groups to be checked. The groups option is a list of groups, and a group is a list of binary operators. Default operator groups are defined as arithmetic, bitwise, comparison, logical, and relational operators. Note: Ternary operator(?😃 can be part of any group and by default is allowed to be mixed with other operators.

  • allowSamePrecedence (boolean) - specifies whether to allow mixed operators if they are of equal precedence. Default is true.

groups

The following operators can be used in groups option:

  • Arithmetic Operators: "+", "-", "*", "/", "%", "**"
  • Bitwise Operators: "&", "|", "^", "~", "<<", ">>", ">>>"
  • Comparison Operators: "==", "!=", "===", "!==", ">", ">=", "<", "<="
  • Logical Operators: "&&", "||"
  • Coalesce Operator: "??"
  • Relational Operators: "in", "instanceof"
  • Ternary Operator: ?:

Now, consider the following group configuration: {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}. There are 2 groups specified in this configuration: bitwise operators and logical operators. This rule checks if the operators belong to the same group only. In this case, this rule checks if bitwise operators and logical operators are mixed, but ignores all other operators.

Examples of incorrect code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]} option:

js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/

var foo = a 
&&
b < 0
||
c > 0 || d + 1 === 0;
var foo = a
&
b
|
c;
incorrect
js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"groups": [["&&", "||", "?:"]]}]*/

var foo = a 
||
b
?
c : d;
var bar = a
?
b
||
c : d;
var baz = a
?
b : c
||
d;
incorrect

Examples of correct code for this rule with {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]} option:

js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"groups": [["&", "|", "^", "~", "<<", ">>", ">>>"], ["&&", "||"]]}]*/

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;
correct
js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"groups": [["&&", "||", "?:"]]}]*/

var foo = (a || b) ? c : d;
var foo = a || (b ? c : d);

var bar = a ? (b || c) : d;

var baz = a ? b : (c || d);
var baz = (a ? b : c) || d;
correct

allowSamePrecedence

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

js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"allowSamePrecedence": true}]*/

// + and - have the same precedence.
var foo = a + b - c;
correct

Examples of incorrect code for this rule with {"allowSamePrecedence": false} option:

js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"allowSamePrecedence": false}]*/

// + and - have the same precedence.
var foo = a 
+
b
-
c;
incorrect

Examples of correct code for this rule with {"allowSamePrecedence": false} option:

js
/*eslint @stylistic/js/no-mixed-operators: ["error", {"allowSamePrecedence": false}]*/

// + and - have the same precedence.
var foo = (a + b) - c;
correct

When Not To Use It

If you don't want to be notified about mixed operators, then it's safe to disable this rule.

Released under the MIT License.