JavaScript for/in Statement

Loop through the properties of an object:

var person = {fname:"John", lname:"Doe", age:25};

var text = "";
var x;
for (x in person) {
text += person[x] + " ";
}

Definition and Usage

The for/in statement loops through the properties of an object.

The block of code inside the loop will be executed once for each property.

JavaScript supports different kinds of loops:

for - loops through a block of code a number of times
for/in - loops through the properties of an object
for/of - loops through the values of an iterable object
while - loops through a block of code while a specified condition is true
do/while - loops through a block of code once, and then repeats the loop while a specified condition is true

Note: Do not use the for/in statement to loop through arrays where index order is important. Use the for statement instead.

Statement
for/in	Yes	Yes	Yes	Yes	Yes

for (var in object) {
code block to be executed
}

Parameter	Description
var	Required. A variable that iterates over the properties of an object
object	Required. The specified object that will be iterated

JavaScript Version:	ECMAScript 1

JavaScript Tutorial: JavaScript For Loop