javascript data types
JavaScript Data Types
In JavaScript there are 3 Primitive datatypes, 2 composite data types, and 2 special data types.
1) Primitive Data Types:
i) String
ii) Number
iii) Boolean
2) Composite data types (reference)
i) Object
ii) Array
3) Special Data types
i)Null
ii) undefined.
1) Primitive Data Types:
a) String:
A string value is a chain of zero or more unicode characters (letters, digits, and punctuation marks). We use the string data type to represent text in Java Script. You include string
literals in scripts by enclosing them in single or double quotation marks.
We can use quotes inside a string, as long as they don't match the quotes surrounding the string.
var answer= " It's alright";
var answer= " He is called 'Sachin'";
var answer = ' He is called "Sachin"';
Notice the javascript does not have a type to represent the single character.
b) Number Data Type:
In javascript, there is no distinction between inter and floating values; a javascript number can be either (internally, javascript represents all numbers as floating-point values).
i)Integer Values:
Integer values can be positive whole numbers, negative whole numbers, and 0. They can be represented in base 10 (decimal), base 16 (hexadecimal), and base 8 (octal). Most numbers in JavaScript are written in decimal.
ii)Floating-point values:
In JavaScript there are 3 Primitive datatypes, 2 composite data types, and 2 special data types.
1) Primitive Data Types:
i) String
ii) Number
iii) Boolean
2) Composite data types (reference)
i) Object
ii) Array
3) Special Data types
i)Null
ii) undefined.
1) Primitive Data Types:
a) String:
A string value is a chain of zero or more unicode characters (letters, digits, and punctuation marks). We use the string data type to represent text in Java Script. You include string
literals in scripts by enclosing them in single or double quotation marks.
We can use quotes inside a string, as long as they don't match the quotes surrounding the string.
var answer= " It's alright";
var answer= " He is called 'Sachin'";
var answer = ' He is called "Sachin"';
Notice the javascript does not have a type to represent the single character.
b) Number Data Type:
In javascript, there is no distinction between inter and floating values; a javascript number can be either (internally, javascript represents all numbers as floating-point values).
i)Integer Values:
Integer values can be positive whole numbers, negative whole numbers, and 0. They can be represented in base 10 (decimal), base 16 (hexadecimal), and base 8 (octal). Most numbers in JavaScript are written in decimal.
You denote hexadecimal ("hex") integers
by prefixing them with a leading "0x" (zero and x|X). They can
contain digits 0 through 9, and letters A through F (either uppercase or
lowercase) only. The letters A through F are used to represent, as single
digits, 10 through 15 in base 10. That is, 0xF is equivalent to 15, and 0x10 is
equivalent to 16.
You denote octal integers by prefixing them with a
leading "0" (zero). They can contain digits 0 through 7 only. A
number that has a leading "0" and contains the digits "8"
and/or "9" is interpreted as a decimal number.
Both hexadecimal and octal numbers can be negative,
but they cannot have a decimal portion, and they cannot be written in
scientific (exponential) notation.
Floating-point values can be whole numbers with a decimal
portion. Additionally, they can be expressed in scientific notation. That is,
an uppercase or lowercase "e" is used to represent "ten to the
power of". JavaScript represents numbers using the eight byte IEEE 754
floating-point standard for numerical representation. This means you can write
numbers as large as 1.79769x10308, and as
small as 5x10-324. A number that contains a
decimal point and that has a single "0" before the decimal point is
interpreted as a decimal floating-point number.
Notice that a number that begins with "0x" or
"00" and contains a decimal point will generate an error. Here are
some examples of JavaScript numbers.
JavaScript contains numbers with special values. These are:
- NaN (not a number). This is
used when a mathematical operation is performed on inappropriate data,
such as strings or the undefined value
- Positive Infinity. This is
used when a positive number is too large to represent in JavaScript
- Negative Infinity. This is
used when a negative number is too large to represent in JavaScript
- Positive and Negative 0.
JavaScript differentiates between positive and negative zero.
iii) Boolean Data Type:
The Boolean data type can only have two. They are the literals true and false. A Boolean value is a truth-value: it specifies
whether the condition is true or not.
Boolean values are especially useful in control structures. The
following code combines a comparison that creates a Boolean value directly with
a statement that uses it. Consider the following JavaScript code sample:
if (x == 2000) {
z = z + 1;
}
else {
x = x + 1;
}
The if/else statement in JavaScript performs one action
if a Boolean value is true (z = z + 1), and an alternate
action if the Boolean value is false(x = x + 1).
You can use any expression as a comparative expression. Any expression
that evaluates to 0, null, undefined, or an empty string is interpreted asfalse.
An expression that evaluates to any other value is interpreted as true.
For example, you could use an expression such as:
// This may not do what you expect. See below!
if (x = y + z)
Note that the above line does not check whether x is equal to y + z, since only a
single equal sign (the assignment operator) is used. Instead, the code above
assigns the value of y + z to the variable x, and then checks
whether the result of the entire expression (the value of x) is zero. To check
whether x is equal to y + z, you need to use the following code.
// This is different from the code above!
if (x == y + z)
2) Composite data types (reference)
Arrays
2) Composite data types (reference)
Arrays
JavaScript
arrays are written with square brackets.
Array
items are separated by commas.
The
following code declares (creates) an array called cars, containing three items
(car names):
Example:
var cars = ["Saab", "Volvo", "BMW"];
Array indexes are zero-based, which means the first
item is [0], second is [1], and so on.
Objects
JavaScript objects are written with curly braces.
i)Null:
The null data type has only one value in JavaScript: null. The null keyword cannot be used as the name of a function or variable.
ii) undefined:
The undefined value is returned when you use an object property that does not exist, or a variable that has been declared, but has never had a value assigned to it.
you can check to see if a variable exists by comparing it to undefined, although you can check if its type is undefined by comparing the type of the variable to the string "undefined".
JavaScript objects are written with curly braces.
Object
properties are written as name:value pairs, separated by commas.
var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
i)Null:
The null data type has only one value in JavaScript: null. The null keyword cannot be used as the name of a function or variable.
A variable that contains null contains no valid Number, String,
Boolean, Array, or Object. You can erase the contents of a variable (without
deleting the variable) by assigning it the null value.
Notice that in JavaScript, null is not the same as 0 (as it is in C
and C++). Also note that the typeof operator in JavaScript reports null values as being of type Object, not of type null. This
potentially confusing behavior is for backwards compatibility.
The undefined value is returned when you use an object property that does not exist, or a variable that has been declared, but has never had a value assigned to it.
you can check to see if a variable exists by comparing it to undefined, although you can check if its type is undefined by comparing the type of the variable to the string "undefined".
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