This chapter describes all JavaScript statements. JavaScript statements consist of keywords used with the appropriate syntax. A single statement may span multiple lines. Multiple statements may occur on a single line if each statement is separated by a semicolon.

Syntax conventions: All keywords in syntax statements are in bold. Words in italics represent user-defined names or statements. Any portions enclosed in square brackets, [ ], are optional. {statements} indicates a block of statements, which can consist of a single statement or multiple statements delimited by a curly braces { }.

Table 3.1 lists statements available in JavaScript.

Table 3.1 JavaScript statements.

`break`	Statement that terminates the current while or for loop and transfers program control to the statement following the terminated loop.
`comment`	Notations by the author to explain what a script does. Comments are ignored by the interpreter.
`continue`	Statement that terminates execution of the block of statements in a while or for loop, and continues execution of the loop with the next iteration.
`delete`	Deletes an object's property or an element of an array.
`do...while`	Executes its statements until the test condition evaluates to false. Statement is executed at least once.
`export`	Allows a signed script to provide properties, functions, and objects to other signed or unsigned scripts.
`for`	Statement that creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a block of statements executed in the loop.
`for...in`	Statement that iterates a specified variable over all the properties of an object. For each distinct property, JavaScript executes the specified statements.
`function`	Statement that declares a JavaScript function name with the specified parameters. Acceptable parameters include strings, numbers, and objects.
`if...else`	Statement that executes a set of statements if a specified condition is true. If the condition is false, another set of statements can be executed.
`import`	Allows a script to import properties, functions, and objects from a signed script which has exported the information.
`labeled`	Provides an identifier that can be used with break or continue to indicate where the program should continue execution.
`return`	Statement that specifies the value to be returned by a function.
`switch`	Allows a program to evaluate an expression and attempt to match the expression's value to a case label.
`var`	Statement that declares a variable, optionally initializing it to a value.
`while`	Statement that creates a loop that evaluates an expression, and if it is true, executes a block of statements.
`with`	Statement that establishes the default object for a set of statements.

break

Terminates the current while or for loop and transfers program control to the statement following the terminated loop.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

break
break label

Argument

label

Identifier associated with the label of the statement.

Description

The break statement can now include an optional label that allows the program to break out of a labeled statement. This type of break must be in a statement identified by the label used by break.

The statements in a labeled statement can be of any type.

Examples

The following function has a break statement that terminates the while loop when e is 3, and then returns the value 3 * x.

function testBreak(x) {
   var i = 0
   while (i < 6) {
      if (i == 3)
         break
      i++
   }
   return i*x
}

In the following example, a statement labeled checkiandj contains a statement labeled checkj. If break is encountered, the program breaks out of the checkj statement and continues with the remainder of the checkiandj statement. If break had a label of checkiandj, the program would break out of the checkiandj statement and continue at the statement following checkiandj.

checkiandj : 
   if (4==i) { 
      document.write("You've entered " + i + ".<BR>");
      checkj : 
         if (2==j) {
            document.write("You've entered " + j + ".<BR>"); 
            break checkj; 
            document.write("The sum is " + (i+j) + ".<BR>"); 
         } 
      document.write(i + "-" + j + "=" + (i-j) + ".<BR>"); 
   }

comment

Notations by the author to explain what a script does. Comments are ignored by the interpreter.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

// comment text
/* multiple line comment text */

Description

JavaScript supports Java-style comments:

Comments on a single line are preceded by a double-slash (//).

Comments that span multiple lines are preceded by a /* and followed by a */.

Examples

// This is a single-line comment.
/* This is a multiple-line comment. It can be of any length, and 
you can put whatever you want here. */

continue

Terminates execution of the block of statements in a while or for loop, and continues execution of the loop with the next iteration.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

continue
continue label

Argument

label

Identifier associated with the label of the statement.

Description

In contrast to the break statement, continue does not terminate the execution of the loop entirely: instead,

In a while loop, it jumps back to the condition.

In a for loop, it jumps to the update expression.

The continue statement can now include an optional label that allows the program to terminate execution of a labeled statement and continue to the specified labeled statement. This type of continue must be in a looping statement identified by the label used by continue.

Examples

The following example shows a while loop that has a continue statement that executes when the value of i is 3. Thus, n takes on the values 1, 3, 7, and 12.

i = 0
n = 0
while (i < 5) {
   i++
   if (i == 3)
      continue
   n += i
}

In the following example, a statement labeled checkiandj contains a statement labeled checkj. If continue is encountered, the program continues at the top of the checkj statement. Each time continue is encountered, checkj reiterates until its condition returns false. When false is returned, the remainder of the checkiandj statement is completed. checkiandj reiterates until its condition returns false. When false is returned, the program continues at the statement following checkiandj.

If continue had a label of checkiandj, the program would continue at the top of the checkiandj statement.

checkiandj : 
while (i<4) {
   document.write(i + "<BR>"); 
   i+=1;

   checkj : 
   while (j>4) {
      document.write(j + "<BR>"); 
      j-=1; 
      if ((j%2)==0)
         continue checkj; 
      document.write(j + " is odd.<BR>");
   } 
   document.write("i = " + i + "<br>");
   document.write("j = " + j + "<br>"); 
}

delete

Deletes an object's property or an element at a specified index in an array.

Implemented in

Navigator 4.0, Netscape Server 3.0

Syntax

delete objectName.property
delete objectName[index]
delete property

Arguments

objectName	An object from which to delete the specified property or value.
property	The property to delete.
index	An integer index into an array.

Description

If the delete operator succeeds, it sets the property of element to undefined; the operator always returns undefined.

You can only use the delete operator to delete object properties and array entries. You cannot use this operator to delete objects or variables. Consequently, you can only use the third form within a with statement, to delete a property from the object.

do...while

Executes its statements until the test condition evaluates to false. Statement is executed at least once.

Implemented in

Navigator 4.0, Netscape Server 3.0

Syntax

do 
   statement
while (condition);

Arguments

statement	Block of statements that is executed at least once and is re-executed each time the condition evaluates to true.
condition	Evaluated after each pass through the loop. If `condition` evaluates to true, the statements in the preceding block are re-executed. When `condition` evaluates to false, control passes to the statement following `do while`.

Example

In the following example, the do loop iterates at least once and reiterates until i is no longer less than 5.

do {
   i+=1
   document.write(i);
while (i<5);

export

Allows a signed script to provide properties, functions, and objects to other signed or unsigned scripts.

Implemented in

Navigator 4.0, Netscape Server 3.0

Syntax

export name1, name2, ..., nameN
export *

Parameters

nameN	List of properties, functions, and objects to be exported.
*	Exports all properties, functions, and objects from the script.

Description

Typically, information in a signed script is available only to scripts signed by the same principals. By exporting properties, functions, or objects, a signed script makes this information available to any script (signed or unsigned). The receiving script uses the companion import statement to access the information.

for

Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a block of statements executed in the loop.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

for ([initial-expression;] [condition;] [increment-expression]) {
   statements
}

Arguments

initial-expression	Statement or variable declaration. Typically used to initialize a counter variable. This expression may optionally declare new variables with the `var` keyword.
condition	Evaluated on each pass through the loop. If this condition evaluates to true, the statements in `statements` are performed. This conditional test is optional. If omitted, the condition always evaluates to true.
increment-expression	Generally used to update or increment the counter variable.
statements	Block of statements that are executed as long as condition evaluates to true. This can be a single statement or multiple statements. Although not required, it is good practice to indent these statements from the beginning of the `for` statement.

Examples

The following for statement starts by declaring the variable i and initializing it to 0. It checks that i is less than nine, performs the two succeeding statements, and increments i by 1 after each pass through the loop.

for (var i = 0; i < 9; i++) {
   n += i
   myfunc(n)
}

for...in

Iterates a specified variable over all the properties of an object. For each distinct property, JavaScript executes the specified statements.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

for (variable in object) {
   statements}

Arguments

variable	Variable to iterate over every property.
object	Object for which the properties are iterated.
statements	Specifies the statements to execute for each property.

Examples

The following function takes as its argument an object and the object's name. It then iterates over all the object's properties and returns a string that lists the property names and their values.

function dump_props(obj, objName) {
   var result = ""
   for (var i in obj) {
      result += objName + "." + i + " = " + obj[i] + "<BR>"
   }
   result += "<HR>"
   return result
}

function

Declares a JavaScript function with the specified parameters. Acceptable parameters include strings, numbers, and objects.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

function name([param] [, param] [..., param]) {
   statements}

Arguments

name	The function name.
param	The name of an argument to be passed to the function. A function can have up to 255 arguments.

Description

To return a value, the function must have a return statement that specifies the value to return. You cannot nest a function statement in another statement or in itself.

All parameters are passed to functions, by value. In other words, the value is passed to the function, but if the function changes the value of the parameter, this change is not reflected globally or in the calling function.

In addition to defining functions as described here, you can also define Function objects.

Examples

//This function returns the total dollar amount of sales, when
//given the number of units sold of products a, b, and c.
function calc_sales(units_a, units_b, units_c) {
   return units_a*79 + units_b*129 + units_c*699
}

if...else

Executes a set of statements if a specified condition is true. If the condition is false, another set of statements can be executed.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

if (condition) {
   statements1}
[else {
   statements2}]

Arguments

condition	Can be any JavaScript expression that evaluates to true or false. Parentheses are required around the condition. If condition evaluates to true, the statements in `statements1` are executed.
statements1 statements2	Can be any JavaScript statements, including further nested `if` statements. Multiple statements must be enclosed in braces.

Examples

if (cipher_char == from_char) {
   result = result + to_char
   x++}
else
   result = result + clear_char

import

Allows a script to import properties, functions, and objects from a signed script which has exported the information.

Implemented in

Navigator 4.0, Netscape Server 3.0

Syntax

import objectName.name1, objectName.name2, ..., objectName.nameN
import objectName.*

Parameters

nameN	List of properties, functions, and objects to import from the export file.
objectName	Name of the object that will receive the imported names.
*	imports all properties, functions, and objects from the export script.

Description

The objectName parameter is the name of the object that will receive the imported names. For example, if f and p have been exported, and if obj is an object from the importing script, then

import obj.f, obj.p

makes f and p accessible in the importing script as properties of obj.

Typically, information in a signed script is available only to scripts signed by the same principals. By exporting (using the export statement) properties, functions, or objects, a signed script makes this information available to any script (signed or unsigned). The receiving script uses the import statement to access the information.

The script must load the export script into a window, frame, or layer before it can import and use any exported properties, functions, and objects.

labeled

Provides an identifier that can be used with break or continue to indicate where the program should continue execution.

Implemented in

Navigator 4.0, Netscape Server 3.0

In a labeled statement, break or continue must be followed with a label, and the label must be the identifier of the labeled statement containing break or continue.

Syntax

label :
   statement

Arguments

statement

Block of statements. break can be used with any labeled statement, and continue can be used with looping labeled statements.

Example

For an example of a labeled statement using break, see break. For an example of a labeled statement using continue, see continue.

return

Specifies the value to be returned by a function.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

return expression

Examples

The following function returns the square of its argument, x, where x is a number.

function square(x) {
   return x * x
}

switch

Allows a program to evaluate an expression and attempt to match the expression's value to a case label.

Implemented in

Navigator 4.0, Netscape Server 3.0

Syntax

switch (expression){
   case label : 
      statement;
      break;
   case label : 
      statement;
      break;
   ...
   default : statement;
}

Arguments

expression	Value matched against label.
label	Identifier used to match against expression.
statement	Any statement.

Description

If a match is found, the program executes the associated statement.

The program first looks for a label matching the value of expression and then executes the associated statement. If no matching label is found, the program looks for the optional default statement, and if found, executes the associated statement. If no default statement is found, the program continues execution at the statement following the end of switch.

The optional break statement associated with each case label ensures that the program breaks out of switch once the matched statement is executed and continues execution at the statement following switch. If break is omitted, the program continues execution at the next statement in the switch statement.

Example

In the following example, if expression evaluates to "Bananas," the program matches the value with case "Bananas" and executes the associated statement. When break is encountered, the program breaks out of switch and executes the statement following switch. If break were omitted, the statement for case "Cherries" would also be executed.

switch (i) {
   case "Oranges" : 
      document.write("Oranges are $0.59 a pound.<BR>"); 
      break; 
   case "Apples" : 
      document.write("Apples are $0.32 a pound.<BR>"); 
      break; 
   case "Bananas" : 
      document.write("Bananas are $0.48 a pound.<BR>"); 
      break; 
   case "Cherries" : 
      document.write("Cherries are $3.00 a pound.<BR>"); 
      break; 
   default : 
      document.write("Sorry, we are out of " + i + ".<BR>"); 
} 
document.write("Is there anything else you'd like?<BR>");

var

Declares a variable, optionally initializing it to a value.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

var varname [= value] [..., varname [= value] ]

Arguments

varname	Variable name. It can be any legal identifier.
value	Initial value of the variable and can be any legal expression.

Description

The scope of a variable is the current function or, for variables declared outside a function, the current application.

Using var outside a function is optional; you can declare a variable by simply assigning it a value. However, it is good style to use var, and it is necessary in functions if a global variable of the same name exists.

Examples

var num_hits = 0, cust_no = 0

while

Creates a loop that evaluates an expression, and if it is true, executes a block of statements. The loop then repeats, as long as the specified condition is true.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

while (condition) {
   statements
}

Arguments

condition	Evaluated before each pass through the loop. If this condition evaluates to true, the statements in the succeeding block are performed. When `condition` evaluates to false, execution continues with the statement following `statements`.
statements	Block of statements that are executed as long as the condition evaluates to true. Although not required, it is good practice to indent these statements from the beginning of the statement.

Examples

The following while loop iterates as long as n is less than three.

n = 0
x = 0
while(n < 3) {
   n ++
   x += n
}

Each iteration, the loop increments n and adds it to x. Therefore, x and n take on the following values:

After the first pass: n = 1 and x = 1

After the second pass: n = 2 and x = 3

After the third pass: n = 3 and x = 6

After completing the third pass, the condition n < 3 is no longer true, so the loop terminates.

with

Establishes the default object for a set of statements. Within the set of statements, any property references that do not specify an object are assumed to be for the default object.

Implemented in

Navigator 2.0, LiveWire 1.0

Syntax

with (object){
   statements
}

Arguments

object	Specifies the default object to use for the statements. The parentheses around object are required.
statements	Any block of statements.

Examples

The following with statement specifies that the Math object is the default object. The statements following the with statement refer to the PI property and the cos and sin methods, without specifying an object. JavaScript assumes the Math object for these references.

var a, x, y
var r=10
with (Math) {
   a = PI * r * r
   x = r * cos(PI)
   y = r * sin(PI/2)
}

(Sebelumnya) Chapter 2. Operators

Chapter 4. Core, Array, Boolean (Berikutnya)

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Chapter 3Statements

break

Syntax

Argument

Description

Examples

See also

comment

Syntax

Description

Examples

continue

Syntax

Argument

Description

Examples

See also

delete

Syntax

Arguments

Description

do...while

Syntax

Arguments

Example

export

Syntax

Parameters

Description

See also

for

Syntax

Arguments

Examples

for...in

Syntax

Arguments

Examples

function

Syntax

Arguments

Description

Examples

if...else

Syntax

Arguments

Examples

import

Syntax

Parameters

Description

See also

labeled

Syntax

Arguments

Example

See also

return

Syntax

Examples

switch

Syntax

Arguments

Description

Example

var

Syntax

Arguments

Description

Examples

while

Syntax

Arguments

Examples

with

Syntax

Arguments

Examples

Chapter 3
Statements