Prefer that
for-in loops should include an if statement JS-0051
Anti-pattern
Minor
2 months ago
—
8 months old
Wrap the body of a for-in loop in an if statement with a hasOwnProperty guard
137 const obj = {} as Record<keyof TOptions, unknown>;
138 const options = optionsCallback(optionsFactory);
139
140 for (const key in options) {141 obj[key] = {142 ...configuration?.[key],143 ...options[key],144 };145 }146
147 return obj as {
148 [key in keyof TOptions]: TOptions[key] & FieldConfiguration<TOptions>;
Description
Looping over objects with a for in loop will include properties that are inherited through the prototype chain.
This behavior can lead to unexpected keys in your for loop.
Bad Practice
for (const key in foo) {
doSomething(key);
}
Recommended
for (const key in foo) {
if (Object.prototype.hasOwnProperty.call(foo, key)) {
doSomething(key);
}
}
for (const key of Object.keys(foo)) {
doSomething(key);
}