for each...in

Выражение for each...in выполняет перебор свойств указанного объекта. Для каждого свойства выполняется указанный оператор.

for each (variable in object) {
  statement
}

variable

Variable to iterate over property values, optionally declared with the var keyword. This variable is local to the function, not to the loop.

object

Object for which the properties are iterated.

statement

A statement to execute for each property. To execute multiple statements within the loop, use a block statement ({ ... }) to group those statements.

Some built-in properties are not iterated over. These include all built-in methods of objects, e.g. String's indexOf method. However, all user-defined properties are iterated over.

Warning: Never use a loop like this on arrays. Only use it on objects. See for...in for more details.

The following snippet iterates over an object's properties, calculating their sum:

var sum = 0;
var obj = {prop1: 5, prop2: 13, prop3: 8};

for each (var item in obj) {
  sum += item;
}

console.log(sum); // logs "26", which is 5+13+8

Not part of a current ECMA-262 specification. Implemented in JavaScript 1.6 and deprecated.

• for each...in удалён только из Nightly Firefox 53

• for...in - аналогичный оператор по перебору имён свойств.
• for...of - аналогичный оператор, перебирающий значения свойств, но может быть использован только для перебираемых (iteratable) типов, so not for generic objects
• for