Javascript learning notes (2) JavaScript core statements

Statement	Syntax	Purpose
Break	Break; BreakLabel;	Exit the innermost loop or switch statement, or exit the label specified statement.
Case	CaseExpression:	Mark a statement in the switch statement
Continue	Continue; ContinueLabel;	Re-start the innermost loop or re-start the cycle specified by label
Default	Default:	Mark the default statement in the switch
Do/while	Do Statement While (Expression);	An alternative form of WHILE LOOP
Empty	;	Do nothing
For	For (Initialize;Test;Increment) Statement	An easy-to-use Loop
For/in	For (VariableInObject) Statement	Traverse the attributes of an object
Function	FunctionFuncname([Arg1[...,Argn]) { Statements }	Declare a function
If/else	If (Expression) Statement1 [ElseStatement2]	Conditional executionCode
Label	Identifier:Statement	ToStatementSpecify a nameIdentifier
Return	Return [Expression];	Returns the value of an expression by a function or by a function.
Switch	Switch (Expression){ Statements }	Use Case orDefault: multi-branch statements marked by statements
Throw	ThrowExpression;	Throw an exception
Try	Try { Statements } Catch (Identifier){ Statements } Finally { Statements }	Capture an exception
VaR	VaRName_1[=Value_1] [,...,Name_n[=Value_n];	Declare and initialize a variable
While	While (Expression) Statement	A basic loop statement
With	With (Object) Statement	Extends the current scope chain (not supported)

Switch language: In JavaScript, the case expression matching the switch language is determined by the = equivalent operator, rather than the = equal operator.

For/in statement: For (variable in object) statement;
Provides a method to traverse object attributes. As follows, for/In cyclically enters all attribute names and their values of an object,
For (VAR prop in my_object ){
Document. Write ("name:" + Prop + "; Value:" + my_object [prop] ");
}
In fact, the for/in loop does not traverse all possible attributes of all objects. Some attributes of an object are marked as read-only, permanent (undeletable), or non-enumerated in the same way. These attributes cannot be enumerated using the for/in loop.

With statement: With statement can greatly reduce the amount of input code, but it runs much slower than the equivalent code that does not use with statement. In addition, function definitions and variable initialization in the with statement may produce unexpected behavior. Therefore, we recommend that you avoid using the with statement.

Null statement: NULL statements do not execute any operations. However, in practice, it is found that null statements are useful when creating a loop with null subjects.