Javascript-4-Javascript as a language I

JavaScript statements are composed of:

Values, Operators, Expressions, Keywords, and Comments.

JavaScript Values are composed of:

• literals. Fixed values are called literals. 
• Numbers(with or without decimals) : Example: 10.5 (or) 10
• Strings(within " or ' quotes). 
• A number in quotes is treated as text : Example: "hello" (or)  'hello'
• the + operator is called the concatenation operator when on Strings.
• If you put a number in quotes, the rest of the numbers will be treated as strings, and concatenated. Example below: 
• <p>The result of adding 2 + 3 + "5":</p>
• <p id="demo"></p>
• <p id="demo2"></p>
• <script>
• var x = 2 + 3 + "5"; 
• document.getElementById("demo").innerHTML = x;
• var x = "2" + 3 + 5; 
• document.getElementById("demo2").innerHTML = x;
• </script>

• O/P : The result of adding 2 + 3 + "5":
  55
  235

• variables. Variable values are called variables. used to store data values.JavaScript uses the var keyword to declare variables. var keyword tells browser to create variables. An equal (=) is used to assign values to variables. Example: var x;x = 6;

JavaScript Expressions:  is a combination of values, variables, and operators, which computes to a value. The computation is called an evaluation. 

Example: 5+6

JavaScript Comments( // or between /* and */):

Example: //var x;

JavaScript Identifiers: identifiers are used to name variables (and keywords, and functions, and labels).

* the first character must be a letter, an underscore (_), or a dollar sign ($).

* Numbers and hyphens are not allowed as the first character.

* identifiers are case-sensitive.

JavaScript ignores multiple whitespaces.

JavaScript Keywords: JavaScript keywords are reserved words. Reserved words cannot be used as names for variables.

Examples : break, continue, if, else, function, var, while,debugger,for, return, switch, try, catch, etc 

var variable: 

• "declaring" a variable.  Example: var x; After the declaration, the variable has no value. it has the value of undefined .
• You can declare many variables in one statement. Example: var person = "John Doe", carName = "Volvo", price = 200;
• If you re-declare a JavaScript variable, it will not lose its value. Example: var person = "John Doe"; var person; If This still assigns the value of  "John Doe" to variable person .