Rule: forin

Requires a for ... in statement to be filtered with an if statement.

Rationale

for (let key in someObject) {
    if (someObject.hasOwnProperty(key)) {
        // code here
    }
}

Prevents accidental iteration over properties inherited from an object’s prototype. See MDN’s for...in documentation for more information about for...in loops.

Also consider using a Map or Set if you’re storing collections of objects. Using Objects can cause occasional edge case bugs, such as if a key is named “hasOwnProperty”.

Config

Not configurable.

Config examples

"forin": true

Schema

null