JavaScript For..In Loop

JavaScript For..In Loop
0

#1

The for..in statement iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.

for (variable in object) {
...
}
Required/Optional Parameter Description
Required Variable A different property name is assigned to variable on each iteration.
Optional Object Object whose enumerable properties are iterated.

MDN link | MSDN link

Examples

// Initialize object.
a = {"a" : "Athens" , "b" : "Belgrade", "c" : "Cairo"}

// Iterate over the properties.
var s = ""
for (var key in a) {
    s += key + ": " + a[key];
    s += "<br />";
    }
document.write (s);

// Output:
// a: Athens
// b: Belgrade
// c: Cairo
// Initialize the array.
var arr = new Array("zero","one","two");

// Add a few expando properties to the array.
arr["orange"] = "fruit";
arr["carrot"] = "vegetable";

// Iterate over the properties and elements.
var s = "";
for (var key in arr) {
    s += key + ": " + arr[key];
    s += "<br />";
}

document.write (s);

// Output:
//   0: zero
//   1: one
//   2: two
//   orange: fruit
//   carrot: vegetable

#2