© 2023 AposTube

Learn JS #24

June 14 • 5:42 pm

Tags:

JavaScript For In

The For In Loop

The JavaScript for in statement loops through the properties of an Object:

Syntax

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

Example

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

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

Example Explained

  • The for in loop iterates over a person object
  • Each iteration returns a key (x)
  • The key is used to access the value of the key
  • The value of the key is person[x]

For In Over Arrays

The JavaScript for in statement can also loop over the properties of an Array:

Syntax

for (variable in array) {
  code
}

Example

const numbers = [45, 4, 9, 16, 25];

let txt = "";
for (let x in numbers) {
  txt += numbers[x];
}

Do not use for in over an Array if the index order is important.

The index order is implementation-dependent, and array values may not be accessed in the order you expect.

It is better to use a for loop, a for of loop, or Array.forEach() when the order is important.

Array.forEach()

The forEach() method calls a function (a callback function) once for each array element.

Example

const numbers = [45, 4, 9, 16, 25];

let txt = "";
numbers.forEach(myFunction);

function myFunction(value, index, array) {
  txt += value;
}

Note that the function takes 3 arguments:

  • The item value
  • The item index
  • The array itself

The example above uses only the value parameter. It can be rewritten to:

Example

const numbers = [45, 4, 9, 16, 25];

let txt = "";
numbers.forEach(myFunction);

function myFunction(value) {
  txt += value;
}

Apostube

See author's posts

Categories

Prev
Next

208 Responses

  100. Everything what you want to know about pills. drug information and news for professionals and consumers.
    ivermectin 5
    Get warning information here. Learn about the side effects, dosages, and interactions.

    Reply

  110. earch our drug database. Everything what you want to know about pills.
    ivermectin generic
    Drugs information sheet. Comprehensive side effect and adverse reaction information.

    Reply

  171. Commonly Used Drugs Charts. Everything information about medication.
    canadian drugs
    Top 100 Searched Drugs. drug information and news for professionals and consumers.

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

© 2023 AposTube. Built with ❤️ using WordPress and Ketos Theme.