prefer-negative-index.md

Prefer negative index over .length - index when possible

💼 This rule is enabled in the ✅ recommended config.

🔧 This rule is automatically fixable by the --fix CLI option.

Prefer negative index over calculating from .length for:

• String#slice()
• Array#slice()
• TypedArray#slice()
• String#at()
• Array#at()
• TypedArray#at()
• Array#splice()
• Array#toSpliced()
• Array#with()
• TypedArray#with()
• TypedArray#subarray()

Fail

foo.slice(foo.length - 2, foo.length - 1);

foo.splice(foo.length - 1, 1);

foo.at(foo.length - 1);

Array.prototype.slice.call(foo, foo.length - 2, foo.length - 1);

Array.prototype.slice.apply(foo, [foo.length - 2, foo.length - 1]);

Pass

foo.slice(-2, -1);

foo.splice(-1, 1);

foo.at(-1);

Array.prototype.slice.call(foo, -2, -1);

Array.prototype.slice.apply(foo, [-2, -1]);

Related rules

• unicorn/prefer-at