Javascript

Statements A-F

Simple statements
Statements make up the backbone of a Javascript program. Each time a variable is created, changed, deleted, or output, each time a function is declared, called or assigned, a statement is created. The following are all examples of simple statements:
var s;
s="Hello, World!";
x=Math.sqrt(4);
y++;

Compound statements
To execute a series of statements as one, use {} brackets. Function declarations, while and for loops and if and switch conditionals all use {} brackets.
y=4; // simple statement if (x==2) { // conditional compound statement y+=x; c=Math.random(); y*=c; }

break
Break from executing the current loop, if more than one, break stops execution of the innermost loop, handing control back to the next innermost. This example code never allows the value of x to exceed 8, despite the loop being able to run to 14.
x=0;
while (x<=14) {
     if (x==8) {break;}
     x++;
}

case
Case is a keyword used to label compound statements within a switch statement.
switch (x) {
case 1 : {y=x;break;}
case 2 : {y=x;}
case 3 :
case 4 : {y=x;break;}
default : {y=0;break;}
}
Note that if x equals 2 or 3, the switch statement continues execution on to the case 4 : statement where the break statement stops further execution.

continue
Continue is used to restart the innermost loop.
x=1;y=1;
while (x<10) {
y++;
if (y==3) break;
else continue;
x++;
}

In this example, the x++ statement is never executed. At the end of the loop, x remains equal to one and y is incremented to 3, at which point the loop reaches break before the continue can be executed. Note that as x is never incremented, the loop must exit using break as the condition while (x<10) will never be met and the loop becomes infinite - your Javascript program will be terminated.

default
default is a keyword used in a switch statement usually as the last in a series of case statements. The default case only executes if no case statement matches the value of the expression in the switch statement.

do
Javascript 1.2 only
Use do to extend the function of the while loop. By default while doesn't execute any code within the loop unless the while condition evaluates to true. If you need the code to execute ONCE even if the while condition doesn't (yet) evaluate to true, use do to enclose the code:
x=1;y=1;
do {
     y++;
     if (y==3) break;
     else continue;
     x++;
}
while (x<10);

for
Simple loops can use for to save code by initialising, testing and incrementing the test conditions in one statement:
for (initialise ; test ; increment) {}

for (x=0;x<10;x++) {}
The loop executes repeatedly until the test condition evaluates to true. Initialisation code is executed once before the first evaluation of the test or the loop. The test condition is evaluated before each loop is executed and the increment expression is executed only once the loop has completed (i.e. just before the next test condition evaluation).

function
Functions are a way of executing compound statements in one HTML or Javascript call with the extra flexibility of passing variables to the function.
function my_func(x,y,z) {
     a=x+y-z;
     alert(a);
}

This function can be called from HTML as:
<a href="javascript:my_func(10,2,3);">Test</a>
Test
In this example, the alert box should show the result as 9.



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