JS Basic Concepts
JavaScript
In this tutorial we will learn about JavaScript Basic Concepts.
Syntax
JavaScript borrows most of its syntax from languages like C/C++, Java, Python etc.
Case sensitive
JavaScript is case-sensitive language. This means lower case letters and upper case letters are treated differently. For example, name and Name are different even though they are the same word.
Instruction
Programs are list of instructions that are executed by the computer. JavaScript programs are instructions that are executed by the web browser.
Statement
JavaScript statements are the instructions written by a programmer.
Semicolon
Every instruction in JavaScript ends with a semicolon ;
In the following example we have an instruction that will print "Hello World" in the browser console.
console.log("Hello World");
Token
The smallest individual unit in a program is called token.
List of JavaScript tokens.
- Reserved Keywords
- Identifiers
- Punctuators
- Literals
Reserved Keywords
Reserved keywords are words that carry a special meaning and must not be used to name variables and functions.
Click here for JavaScript Variables.
Click here for JavaScript Functions.
Following are some of the commonly used JavaScript reserved keywords.
| break | case | const | continue |
| default | delete | do | else |
| false | final | for | function |
| if | instanceof | new | null |
| return | static | switch | this |
| true | typeof | var | while |
Identifiers
Identifiers are sequence of characters that are used to name the variables, functions etc.
Characters of an identifier can be a letter, digit, dollar sign and underscore. The first character cannot be a digit.
- Letter a-z A-Z
- Digit 0-9
- Dollar sign $
- Underscore _
Following are valid identifiers.
name
_name
name$
student01
Following are invalid identifiers.
01student
student-name
student+name
Punctuators
Following are the list of punctuators that we use in JavaScript.
| = | < | > | == | <= | >= | === |
| ! | != | !== | + | - | * | / |
| , | . | % | ~ | ? | : | ; |
| & | && | | | || | ++ | -- | ^ |
| &= | |= | %= | += | -= | *= | /= |
| ^= | << | >> | >>> | <<= | >>= | >>>= |
| ( | ) | [ | ] | { | } |
Literals
We use literals to represent value in JavaScript.
List of literals.
- Null literal
- Boolean literal
- Numeric literal
- String literal
Null literal
The value of the Null literal is null. It represent null or empty.
Boolean literal
The value of the Boolean literal are true and false. These are logical values.
Numeric literal
We use Numeric literal to represent numbers or numerical value.
Following are the types of numerical values.
- Decimal
- Hexadecimal
- Octal
Decimal number are base 10 i.e., they consists of 10 digits 0 to 9.
Hexadecimal number are base 16 i.e., they consists of 10 digits 0 to 9 and 6 letters a to f. Upper case A to F is also used. Hex number start with 0x and 0X.
Example: 0xA is in hex form and its decimal equivalent is 10.
Click here for Hexadecimal to Decimal conversion tutorial.
Octal number are base 8 i.e., they consists of 8 digits 0 to 7. Octal number starts with 0.
Example: 017 is in octal form and its decimal equivalent is 15.
Click here for Octal to Decimal conversion tutorial.
String literal
Strings are sequence of characters enclosed in double and single quote in JavaScript.
In the following example we have a string enclosed in double quote.
"Hello World"
In the following example we have a string enclosed in single quote.
'We are learning JavaScript.'
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