JavaScript provides five scalar primitive types: Number, Boolean, String, Undefined, Null and two compound primitive types Array and Object. Even though JavaScript supports object-orientation features, it still supports these scalar primitive data types simply because of performance reasons. Maintenance of primitive values is much faster than objects.
JavaScript also provides object versions known as wrapper objects for the primitive types Number, Boolean and String namely, Number, Boolean and String. All primitive values are stored on stack whereas objects are stored in heap.
String Data Type
A string literal is a string value enclosed in either double quotes or single quotes. Following are some of the examples of string literals:
“Hello World!”
‘Welcome to JavaScript’
“What is your name?”
‘”JavaScript” and “Java” are different programming languages’
A string with no character is an empty string. JavaScript does not support character data type. A character value is represented as a string containing a single character.
Number Data Type
A variable of type number can hold either integer or real numbers. JavaScript does not differentiate between integers and real numbers. All numbers are stored using 64-bit double precision.
JavaScript provides a special value NaN (Not A Number) that represents an error condition. Many JavaScript functions return this value, if the argument cannot be converted to a number.
Integer literals may be written either in decimal, hexadecimal or octal notation. Examples of decimal integer literals are given below:
2, 100, 0, -1, -200
A hexadecimal integer literal starts with “0x” or “0X”. Following are examples of hexadecimal integer literals:
0x4, -0x2, 0xFF, 0X10, 0XA2
Octal integer literals start with 0 and may contain digits 0 through 7. Following are examples of octal integer literals:
04, 05, 010, -02, 00, 012
Floating point numbers
Floating point numbers are written using base 10. They may contain fractional parts separated by a decimal point. Scientific notation is also allowed. Following are some examples of floating point numbers:
.001, 0.01, 3.4, 4, -2, 2e2, 2.3e4, 2e-3, 4.5e-2
Boolean Data Type
A boolean type variable can hold only two values: true or false. A non-zero value is treated as true and zero is treated as the boolean value false.
Comments
Every programming language supports comments through which a programmer can provide details like author name, creation date and purpose of the script. Apart from these details, comments allow programmers to write explanations or reviews about their script or elements in the script.
A single line comment in JavaScript starts with //. Everything followed by // in that line is treated as a comment.
A single line or multi-line comment starts with /* and ends with */. Everything in between these two markers is treated as a comment and will be ignored by the JavaScript interpreter.
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