avaScript 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 semi-colon.
avaScript 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 semi-colon.
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 {}.
The following statements are available in JavaScript:
|
break
comment continue for for...in function if...else |
new (operator)
return this (operator) var while with |
Note
new and this are not statements, but are included in this section for convenience.
break
function testBreak(x) {
var i = 0
while (i < 6) {
if (i == 3)
break
i++
}
return i*x
}
1. // comment text
2. /* multiple line comment text */
// 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. */
i = 0
n = 0
while (i < 5) {
i++
if (i == 3)
continue
n += i
}
for ([initial-expression;] [condition;] [increment-expression]) {
statements
}
for (var i = 0; i < 9; i++) {
n += i
myfunc(n)
}
for (variable in object) {
statements }
function dump_props(obj, obj_name) {
var result = ""
for (var i in obj) {
result += obj_name + "." + i + " = " + obj[i] + "<BR>"
}
result += "<HR>"
return result
}
Syntax
function name([param] [, param] [..., param]) {
statements } Arguments
name is the function name.
param is the name of an argument to be passed to the function. A function can have up to 255 arguments.
Implemented in
Navigator 2.0
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 (condition) {
statements1 }
[else {
statements2}]
if ( cipher_char == from_char ) {
result = result + to_char
x++ }
else
result = result + clear_char
car1.color = "black" adds a property color to car1, and assigns it a value of "black". However, this does not affect any other objects. To add the new property to all objects of the same type, you must add the property to the definition of the car object type.
You can add a property to a previously defined object type by using the prototype property. This defines a property that is shared by all objects of the specified type, rather than by just one instance of the object. The following code adds a color property to all objects of type car, and then assigns a value to the color property of the object car1. For more information, see "prototype".
Car.prototype.color=null
car1.color="black"
birthday.description="The day you were born" Syntax
objectName = new objectType ( param1 [,param2] ...[,paramN] )
Arguments
objectName is the name of the new object instance.
objectType is the object type. It must be a function that defines an object type.
param1...paramN are the property values for the object. These properties are parameters defined for the objectType function.
Implemented in
Navigator 2.0
Examples
Example 1: object type and object instance. Suppose you want to create an object type for cars. You want this type of object to be called car, and you want it to have properties for make, model, and year. To do this, you would write the following function:
function car(make, model, year) {
Now you can create an object called mycar as follows:
this.make = make
this.model = model
this.year = year
}mycar = new car("Eagle", "Talon TSi", 1993)
This statement creates mycar and assigns it the specified values for its properties. Then the value of mycar.make is the string "Eagle", mycar.year is the integer 1993, and so on.
You can create any number of car objects by calls to new. For example,
kenscar = new car("Nissan", "300ZX", 1992)
Example 2: object property that is itself another object. Suppose you define an object called person as follows:
function person(name, age, sex) {
And then instantiate two new person objects as follows:
this.name = name
this.age = age
this.sex = sex
}rand = new person("Rand McNally", 33, "M")
Then you can rewrite the definition of car to include an owner property that takes a person object, as follows:
ken = new person("Ken Jones", 39, "M")function car(make, model, year, owner) {
To instantiate the new objects, you then use the following:
this.make = make;
this.model = model;
this.year = year;
this.owner = owner;
}car1 = new car("Eagle", "Talon TSi", 1993, rand);
Instead of passing a literal string or integer value when creating the new objects, the above statements pass the objects rand and ken as the parameters for the owners. To find out the name of the owner of car2, you can access the following property:
car2 = new car("Nissan", "300ZX", 1992, ken)car2.owner.name
return expression
function square( x ) {
return x * x
}
this[.propertyName]
function validate(obj, lowval, hival) {
if ((obj.value < lowval) || (obj.value > hival))
alert("Invalid Value!")
}
You could call validate in each form element's onChange event handler, using this to pass it the form element, as in the following example:
<B>Enter a number between 18 and 99:</B>
<INPUT TYPE = "text" NAME = "age" SIZE = 3
onChange="validate(this, 18, 99)">
var varname [= value] [..., varname [= value] ]
var num_hits = 0, cust_no = 0
while (condition) {
statements
}
n = 0Each iteration, the loop increments n and adds it to x. Therefore, x and n take on the following values:
x = 0
while( n < 3 ) {
n ++
x += n
}
n < 3 is no longer true, so the loop terminates.
with (object){
statements
}
var a, x, y
var r=10
with (Math) {
a = PI * r * r
x = r * cos(PI)
y = r * sin(PI/2)
}