JavaScript for...in Loop
Examples
Iterate (loop) over the properties of an object:
constperson = {fname:"John", lname:"Doe", age:25};
let text = "";
for (let x in person) {
text += person[x] + " ";
}
Try it Yourself »
Iterate (loop) over the values of an array:
const cars = ["BMW", "Volvo", "Saab", "Ford"];
let text = "";
for (let x in cars) {
text += cars[x] + " ";
}
Try it Yourself »
More examples below.
Definition and Usage
The for...in statements combo iterates (loops) over the properties of an object.
The code block inside the loop is executed once for each property.
Note
Do not use for...in to iterate an array if the index order is important. Use a for loop instead.
See Also:
Syntax
for (x in
object) {
code block to be executed
}
Parameters
| Parameter | Description |
| x | Required. A variable to iterate over the properties. |
| object | Required. The object to be iterated |
JavaScript Loop Statements
| Statement | Description | |
| break | Breaks out of a loop | |
| continue | Skips a value in a loop | |
| while | Loops a code block while a condition is true | |
| do...while | Loops a code block once, and then while a condition is true | |
| for | Loops a code block while a condition is true | |
| for...of | Loops the values of any iterable | |
| for...in | Loops the properties of an object |
More Examples
Iterate over the properties of window.location:
let text = "";
for (let x in location) {
text += x + "
";
}
document.getElementById("demo").innerHTML = text;
Try it Yourself »
Browser Support
for...in is an ECMAScript1 (ES1) feature.
ES1 (JavaScript 1997) is fully supported in all browsers:
| Chrome | IE | Edge | Firefox | Safari | Opera |
| Yes | Yes | Yes | Yes | Yes | Yes |
