JavaScript Statement Classification Encyclopedia

Core tips: JavaScript Statement Classification Encyclopedia

1, assignment statement: Var

2.return statement

3, Conditional branch statement If...else,switch

4, circular statement for,for...in,while,break,continue.

5, the object operation statement With,new,delete,this

6. Comment Statement

7. Function definition statement: Function,return

1. Variable declaration assignment statement: VAR

The Var statement declares the name of a variable and can also have an initial value for that variable.

If the Var statement declares a variable in a function, the valid region of the variable is limited to this function, called a local variable, and if the Var statement is outside the function body, the active area is the entire application, called the global variable.

It is possible to declare a variable outside the function body without using VAR and give the value of the variable. (but Var is recommended)

The syntax for VAR is as follows:

Cases:

　

var computer=9//computer is an integer variable with an initial value of 9 Computer=9//computer is an integer variable with an initial value of 9

2.return statement

The return statement indicates the value that will be returned by the function.

The syntax is as follows:

return expression;

If the expression is omitted here, or there is no return statement at the end of the function, this function returns a value of the undefined type.

3, Conditional branch statement If...else,switch

1.if...else

1) Basic format

if (expression)

statement paragraph 1;

......

Else

statement paragraph 2;

......

2 function: If the expression is true, then execute the statement paragraph 1, otherwise execute statement paragraph 2.

3) Description:

The if-else statement is the most basic control statement in JavaScript, which allows you to change the order in which statements are executed.

• The expression must use a relational statement to implement the judgment, which is evaluated as a Boolean value.

• It converts 0 and nonzero numbers to false and true respectively.

• If the statement after if has more than one line, you must enclose it with curly braces.

4 Nesting of IF statements

if (Boolean) statement 1;

Else (Boolean) statement 2;

else if (Boolean) statement 3;

......

Else Statement 4;

In this case, each level of the Boolean expression will be computed, if true, then execute its corresponding statement, otherwise execute else after the statement.

Example:

<script> function ABCD () { var d=confirm ("Please select OK or cancel"); if (d==1) { Alert ("You choose to be sure"); } else{ Alert ("You choose to cancel"); } } </script>

5). Switch statement

A branch statement switch can take a different approach depending on the value of a variable.

The syntax for the switch is as follows:

switch (expression) {

Case Label 1:

Execute the statement;

Case Label 2:

Execute the statement;

......

Default:

Execute the statement;

}

Example:

<script> var d= new Date (); Switch (d.getdate ()) { Case 0:document.write ("Monday"); Case 1:document.write ("Tuesday"); Case 2:document.write ("Wednesday"); Case 3:document.write ("Thursday"); Case 4:document.write ("Friday"); Case 5:document.write ("Saturday"); Case 6:document.write ("Sunday"); } </script>

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