{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 |
new
|
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
}
function name([param] [, param] [..., param]) {
statements }
//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
To define an object type, create a function for the object type that specifies its name, properties, and methods. An object can have a property that is itself another object. See the examples below.
You can always add a property to a previously defined object. For example, the statement 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.
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.
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, year, and color. To do this, you would write the following function:
function car(make, model, year) {
this.make = make
this.model = model
this.year = year
}
Now you can create an object called mycar as follows:
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) {
this.name = name
this.age = age
this.sex = sex
}
And then instantiate two new person objects as follows:
rand = new person("Rand McNally", 33, "M")
ken = new person("Ken Jones", 39, "M")
Then you can rewrite the definition of car to include an owner property that takes a person object, as follows:
function car(make, model, year, owner) {
this.make = make;
this.model = model;
this.year = year;
this.owner = owner;
}
To instantiate the new objects, you then use the following:
car1 = new car("Eagle", "Talon TSi", 1993, rand);
car2 = new car("Nissan", "300ZX", 1992, ken)
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.owner.name
return
A statement that specifies the value to be returned by a function.
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
}
this
A keyword that you can use to refer to the current object. In general, in a method this refers to the calling object.
Syntax
this[.propertyName]
Examples
Suppose a function called validate validates an object's value property, given the object and the high and low values:
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
A statement that declares a variable, optionally initializing it to a value. 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.
Syntax
var varname [= value] [..., varname [= value] ]
Arguments
varname is the variable name. It can be any legal identifier.
value is the initial value of the variable and can be any legal expression.
Examples
var num_hits = 0, cust_no = 0
while
A statement that 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.
Syntax
while (condition) {
statements
}
Arguments
condition is 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 is a 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 while 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:
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)
}