JavaScript statement identifier, variable period

Statement	Description
Break	Used to jump out of a loop.
Catch	Statement block that executes a catch statement block when a try statement block performs an error.
Continue	Skips an iteration in the loop.
Do ... while	Executes a block of statements that continues executing the statement block when the condition statement is true.
For	When the conditional statement is true, the code block can be executed a specified number of times.
For ... in	Used to iterate over an array or an object's properties (to iterate over a group or an object's properties).
function	Define a function
If ... else	Used to perform different actions based on different conditions.
Return	Exit function
Switch	Used to perform different actions based on different conditions.
Throw	Throws (generates) an error.
Try	Implements error handling and is used with catch.
Var	Declares a variable.
While	When the conditional statement is true, the statement block is executed.

The lifetime of a JavaScript variable

The lifetime of JavaScript variables begins at the time they are declared.

Local variables are deleted after the function is run.

Global variables are deleted after the page is closed.

Common HTML Events

Events	Description
OnChange	HTML element Changes
OnClick	User clicks on HTML element
onmouseover	The user moves the mouse over an HTML element
onmouseout	The user moves the mouse away from an HTML element
OnKeyDown	The user presses the keyboard key
OnLoad	The browser has finished loading the page

JavaScript tags

As you saw in the switch statement chapter, you can tag JavaScript statements.

To mark a JavaScript statement, precede the statement with a colon:

label: statements

The break and continue statements are just statements that can jump out of a block of code.

Grammar:

break labelname; continue labelname;

Continue statements (with or without label references) can only be used in loops.

The break statement (without a label reference) can only be used in loops or switch.

With a label reference, the break statement can be used to jump out of any JAVASCRIPT code block:

Instance

cars=["BMW", "Volvo", "Saab", "Ford"];list: {document.write (cars[0] + "<BR>"); document.write (Cars[1] + "<BR>"); document.write (cars[2] + "<BR>");    Break list; document.write (Cars[3] + "<BR>"); document.write (Cars[4] + "<BR>"); document.write (Cars[5] + "<BR>"); }

JavaScript Data types

There are 5 different types of data in JavaScript:

• String
• Number
• Boolean
• Object
• function

3 Types of objects:

• Object
• Date
• Array

2 data types that do not contain any values:

• Null
• Undefinedconstructor Property

  The constructor property returns the constructor for all JavaScript variables.

  Convert a string to a number

  The global Method number () converts the string to numbers.

  strings that contain numbers (such as "3.14") are converted to numbers (such as 3.14).

  The empty string is converted to 0.

  The other strings are converted to NaN (not a number).

  Method	Description
  Parsefloat ()	Parses a string and returns a floating-point number.
  parseint ()	Parses a string and returns an integer.

JavaScript statement identifier, variable period