Description

Many built-in data structures (ex. Map) expose an iterator with the well known @@iterator (Symbol.iterator) key and the #entries() instance method.

Some built-in data structures (ex. Array) are the same but with @@iterator and #values().

Some built-in data structures (ex. Set) are the same but with @@iterator and #keys().

Some built-in data structures support all 3 methods for the same iterator. I think Set is the only one that does this.

Having a rule to ensure consistent usage of these iterators can be helpful for maintaining convention in a codebase.

Fail

When preferring @@iterator:

for (const x of map.entries()) {}

[...map.entries()];

new Map(map.entries());

[...array.values()];

When preferring #entries(), #values(), or #keys():

for (const x of map) {}

[...map];

new Map(map);

[...array];

Pass

When preferring #entries(), #values(), or #keys():

for (const x of map.entries()) {}

[...map.entries()];

new Map(map.entries());

When preferring @@iterator:

for (const x of map) {}

[...map];

new Map(map);

Additional Info

Built-in data structures that should support @@iterator and #entries():

• Map
• Set
• FormData (the global, not the one from form-data)
• URLSearchParams

Built-in data structures that should support @@iterator and #values():

• Array
• Set
• TypedArray

Built-in data structures that should support @@iterator and #keys():

• Set