Code Inspection: Unfiltered for..in loop

Reports unfiltered for-in loops.

The use of this construct results in processing not only own properties of an object but properties from its prototype as well. It may be unexpected in some specific cases, for example, in utility methods that copy or modify all properties or when Object 's prototype may be incorrectly modified. For example, the following code will print 42 and myMethod:

Object.prototype.myMethod = function myMethod() {};
let a = { foo: 42 };
for (let i in a) {
  console.log(a[i]);
}

Suggests replacing the whole loop with a Object.keys() method or adding a hasOwnProperty() check. After applying the quick-fix the code looks as follows:

for (let i in a) {
  if (a.hasOwnProperty(i)) {
    console.log(a[i]);
  }
}

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Place the caret at the highlighted line and press Alt+Enter or click .
Click the arrow next to the inspection you want to suppress and select the necessary suppress action.

Last modified: 17 April 2024