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The web page uses the HTML preformatted text tags to prevent the formatting character from being treated as HTML white space characters notice that the backspace character is incorrectly displayed, the form feed character is ignored, and that the carriage return character is displayed in the same manner as the new line character. Even though these characters are not fully supported in the display of Web page, they may still be used to insert formatting codes within data and files that JavaScript produced. The null value. The null value is common to all JavaScript types. It is used to set a variable to an initial value that is different from other valid values. The use of the null value prevented the sort of error that result from using uninitialized variables. The null value is automatically converted to default values of others types when used in an expression, as you will see in the following section," Conversion between Types.



The undefined value



The undefined value indicates that a variable has been created but not assigned a value. Like the null value, the undefined value is common to all JavaScript types and is automatically converted to default value of these types. The undefined value is converted to NaN for numeric types false for Boolean, and "undefined "for strings. Conversion between Types JavaScript is automatically convert values from one type to another when they are used in an expression. This means that you can combine different type in an expression and JavaScript will try to perform the type conversion that are necessary for the expression to make sense. How does JavaScript convert from one to another? The process of determining when a conversion should accrue and what type of conversion should be made is fairly complex. JavaScript convert value when it evaluates an expressions or assign a value to a variable when JavaScript assign a value to a variable it change the types associated with the variable to the type of the value at this assigns.



When JavaScript evaluates an expression, it parses expression into its components unary and binary expression based upon the order of precedence of the operator it contains. It then evaluates the component unary and binary expression is evaluated according to the operators involved. If an operator takes a value of a type that is different than the type of operand is converted to a type that is valid for the operator. Some operator, such as the +operator, may be used for more than one type.

The script in the document head defines the variables to be used in the table’s operations. The s1 and s2 variable are assigned string values. The script in the document body long. However, most of the script is used to generate the HTML tags for the cell of the conversion table. The script is surrounded by the tag and the script is then generates the cell of the table one row at a time. First, the column header row is displayed. Then each row of the table.

The Historical Relationship between HTML and XML



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