Rule proposal: Prefer .includes()

[sindresorhus]

This rule should prefer .includes() over .indexOf() when checking for existence. This would apply to the following types: String#includes, Array#includes, TypedArray#includes, Buffer#includes.

.includes() cases:

• 'foobar'.indexOf('foo') !== -1
• 'foobar'.indexOf('foo') != -1
• 'foobar'.indexOf('foo') > -1
• 'foobar'.indexOf('foo') >= 0

_{These would negate .includes():}

• 'foobar'.indexOf('foo') == -1
• 'foobar'.indexOf('foo') === -1
• 'foobar'.indexOf('foo') < 0

It would also be useful to catch cases where String#includes() would be better than a regex: /\r\n/.test(foo); => foo.includes('\r\n');

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This was originally proposed for inclusion in ESLint, but declined for lack of type knowledge in JS.

[mysticatea]

I will work on this.

I think that I'd like to separate this to two rules:

• prefer-array-includes ... for Array, ReadonlyArray, typed arrays, and child classes of those (Buffer extends Uint8Array). Array#includes has been added in ES2016.
• prefer-string-includes ... for strings. This address regular expressions as suggested. String#includes has been added in ES2015.

Thoughts?

[mysticatea]

After re-tought, I will go with one rule:

• prefer-includes ... for all types which have both indexOf method and includes method, if the parameter types of those methods are same completely, the rule suggests to use includes method.