72 lines
1.8 KiB
Markdown
72 lines
1.8 KiB
Markdown
|
---
|
||
|
title: For...In Loop
|
||
|
---
|
||
|
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. |
|
||
|
|
||
|
|
||
|
|
||
|
## 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
|
||
|
|
||
|
// Efficient way of getting an object's keys using an expression within the for-in loop's conditions
|
||
|
var myObj = {a: 1, b: 2, c:3}, myKeys = [], i=0;
|
||
|
for (myKeys[i++] in myObj);
|
||
|
|
||
|
document.write(myKeys);
|
||
|
|
||
|
//Output:
|
||
|
// a
|
||
|
// b
|
||
|
// c
|
||
|
|
||
|
# Ohter Resources:
|
||
|
* [MDN link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in)
|
||
|
* [MSDN link](https://msdn.microsoft.com/library/55wb2d34.aspx)
|