JS.BASE.OPERATOR.ASSIGNMENT
Require or disallow assignment operator shorthand where possible
JavaScript provides shorthand operators that combine variable assignment and some simple mathematical operations. For example, x = x + 4 can be shortened to x += 4. The supported shorthand forms are as follows:
Shorthand | Separate
-----------|------------
x += y | x = x + y
x -= y | x = x - y
x *= y | x = x * y
x /= y | x = x / y
x %= y | x = x % y
x **= y | x = x ** y
x <<= y | x = x << y
x >>= y | x = x >> y
x >>>= y | x = x >>> y
x &= y | x = x & y
x ^= y | x = x ^ y
x |= y | x = x | y
Rule Details
This rule requires or disallows assignment operator shorthand where possible.
The rule applies to the operators listed in the above table. It does not report the logical assignment operators &&=, ||=, and ??= because their short-circuiting behavior is different from the other assignment operators.
Options
This rule has a single string option:
"always"(default) requires assignment operator shorthand where possible"never"disallows assignment operator shorthand
always
Examples of incorrect code for this rule with the default "always" option:
/*eslint operator-assignment: ["error", "always"]*/
x = x + y;
x = y * x;
x[0] = x[0] / y;
x.y = x.y << z;
Examples of correct code for this rule with the default "always" option:
/*eslint operator-assignment: ["error", "always"]*/
x = y;
x += y;
x = y * z;
x = (x * y) * z;
x[0] /= y;
x[foo()] = x[foo()] % 2;
x = y + x; // `+` is not always commutative (e.g. x = "abc")
never
Examples of incorrect code for this rule with the "never" option:
/*eslint operator-assignment: ["error", "never"]*/
x *= y;
x ^= (y + z) / foo();
Examples of correct code for this rule with the "never" option:
/*eslint operator-assignment: ["error", "never"]*/
x = x + y;
x.y = x.y / a.b;
When Not To Use It
Use of operator assignment shorthand is a stylistic choice. Leaving this rule turned off would allow developers to choose which style is more readable on a case-by-case basis.