heading JavaScript Literals

JavaScript : Array literals

In Javascript, an array literal is a list of expressions, each of which represents an array element, enclosed in a pair of square brackets ' [ ] ' . When an array is created using an array literal, it is initialized with the specified values as its elements, and its length is set to the number of arguments specified. If no value is supplied it creates an empty array with zero length.

Creating an empty array :

var fruits = [ ];

Creating an array with four elements.

var fruits = ["Orange", "Apple", "Banana", "Mango"]

Comma in array literals

There is no need to specify all elements in an array literal. If we put two commas in a row at any position in an array then an unspecified element will be created in that place.

The following example creates the fruits array :

fruits = ["Orange", , "Mango"]

This array has one empty element in the middle and two elements with values. ( fruits[0] is "Orange", fruits[1] is set to undefined, and fruits[2] is "Mango").

If you include a single comma at the end of the elements, the comma is ignored. In the following example, the length of the array is three. There are no fruits[2].

fruits = ["Orange", "Mango",]

In the following example, the length of the array is four, and fruits[0] and fruits[2] are undefined.

fruits = [ , 'Apple', , 'Orange'];

JavaScript: Integers literals


An integer must have at least one digit (0-9).

  • No comma or blanks are allowed within an integer.
  • It does not contain any fractional part.
  • It can be either positive or negative if no sign precedes it is assumed to be positive.

In JavaScript, integers can be expressed in three different bases.

1. Decimal ( base 10)

Decimal numbers can be made with the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and there will be no leading zeros.

Example: 123, -20, 12345

2. Hexadecimal ( base 16)

Hexadecimal numbers can be made with the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and letters A, B, C, D, E, F or a, b, c, d, e, f. A leading 0x or 0X indicates the number is hexadecimal.

Example: 7b, -14, 3039

3. Octal (base 8)

Octal numbers can be made with the digits 0, 1, 2, 3, 4, 5, 6, 7. A leading 0 indicates the number is octal.

Example: 173, -24, 30071

JavaScript: Floating number literals


A floating number has the following parts.

  • A decimal integer.
  • A decimal point ('.').
  • A fraction.
  • An exponent.

The exponent part is an "e" or "E" followed by an integer, which can be signed (preceded by "+" or "-").

Example of some floating numbers :

  • 8.2935
  • -14.72
  • 12.4e3 [ Equivalent to 12.4 x 103 ]
  • 4E-3 [ Equivalent to 4 x 10-3 => .004 ]

JavaScript: Boolean literals

The Boolean type has two literal values:

  • true
  • false

JavaScript: Object literals


An object literal is zero or more pairs of comma-separated list of property names and associated values, enclosed by a pair of curly braces.

In JavaScript an object literal is declared as follows:

1. An object literal without properties:

var userObject = {}

2. An object literal with a few properties :

var student = {
First-name : "Suresy",
Last-name : "Rayy",
Roll-No : 12

Syntax Rules

Object literals maintain the following syntax rules:

  • There is a colon (:) between property name and value.
  • A comma separates each property name/value from the next.
  • There will be no comma after the last property name/value pair.

JavaScript: String literals


JavaScript has its own way to deal with string literals. A string literal is zero or more characters, either enclosed in single quotation (') marks or double quotation (") marks. You can also use + operator to join strings. The following are the examples of string literals :

  • string1 = "w3resource.com"
  • string1 = 'w3resource.com'
  • string1 = "1000"
  • string1 = "google" + ".com"

In addition to ordinary characters, you can include special characters in strings, as shown in the following table.

string1 = "First line. \n Second line."

List of special characters used in JavaScript string:

Character Meaning
\b Backspace
\f Form feed
\n New line
\r Carriage return
\t Tab
\' Single quote
\" Double quote
\\ Backslash character (\)
\XXX The character with the Latin-1 encoding specified by up to three octal digits XXX between 0 and 377. For example, \100 is the octal sequence for the @ symbol.
\xXX The character with the Latin-1 encoding specified by the two hexadecimal digits XX between 00 and FF. For example, \x40 is the hexadecimal sequence for the @ symbol.
\uXXXX The Unicode character specified by the four hexadecimal digits XXXX. For example, \u0040 is the Unicode sequence for the @ symbol.

Previous: JavaScript : Variables, Constants, Data Type and Reserved Words
Next: JavaScript: Color Values

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JavaScript: Tips of the Day

object keys

const obj = { 1: 'a', 2: 'b', 3: 'c' };
const set = new Set([1, 2, 3, 4, 5]);


All object keys (excluding Symbols) are strings under the hood, even if you don't type it yourself as a string. This is why obj.hasOwnProperty('1') also returns true.
It doesn't work that way for a set. There is no '1' in our set: set.has('1') returns false. It has the numeric type 1, set.has(1) returns true.

Ref: https://bit.ly/323Y0P6