JavaScript: for in Statement

Last update on May 28 2022 10:26:50 (UTC/GMT +8 hours)

Description

The for...in statement iterates (the act of repeating a process) a specified variable over all the properties of an object and execute one or more statements for each property of the object.

Syntax

for (variable in object)
{
statements
}

Parameters

Variable: Variable to iterate over every property of the object and the variable is accessible outside the loop, after completing the loop.

statements : The statement to be executed for each property of an object. For multiple statements within the loop use a block statement ({..}).

Example:

In the following web document for in statement iterates a specified variable over all the properties of an object.

HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset=utf-8>
<title>JavaScript for in statement :  Example-1</title>
<link rel="stylesheet" type="text/css" href="example.css">
</head>
<body>
<h1>JavaScript : for in statement </h1>
<p id="result">Output will be displayed here.</p>
<script src="for-in-statement-example1.js"></script>
</body>
</html>

JS Code

function demo()
{
var  key, str1 = "";
// Initialize object.
var student = {
name : "David Rayy",
classname : "V",
rollno : 12
};
// Iterate the properties.
for(key in student)
{
str1 = str1+ student[key];
}
return(str1);
}
var newParagraph = document.createElement("p");
var newText = document.createTextNode(demo());
newParagraph.appendChild(newText);
document.body.appendChild(newParagraph);

View the example in the browser

Practice the example online

See the Pen for-in-1 by w3resource (@w3resource) on CodePen.

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Next: JavaScript: try...catch statement

JavaScript: Tips of the Day

How to insert an item into an array at a specific index (JavaScript)?

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:

var arr = []; arr[0] = "Jani"; arr[1] = "Hege"; arr[2] = "Stale"; arr[3] = "Kai Jim"; arr[4] = "Borge"; console.log(arr.join()); arr.splice(2, 0, "Lene"); console.log(arr.join());

Ref: https://bit.ly/2BXbp04