Basic JavaScript Loops
It often happens that you have to execute code blocks multiple times. You can do this effectively using JavaScript loops.
For loops
This loop usually executes a command a certain number of times. You use statements to define the amount of times the command is executed. For loops have the following base-syntax:
for(initialization/start-value; condition; command){
//code block
}
As you can see, the for loop contains 3 parameters that are used to define how often the code block is executed:
-
Initialization/counting variable
With this parameter you define a counting variable and its start-value. Multiple variables have to be separated by commas.
-
Condition
The for loop is executed as long as this condition is true.
-
Command
This command is executed every time after the execution of the code block.
The following code writes Toolinfy 5 times.
for(i=0; i<5; i++){
document.write("Toolinfy <br/>");
}
This code transformed into an actual sentence would be something like: "As long as i
is smaller than 5 write Toolinfy and increment i
by 1."
The counting variable can also be used in the code block. In the following example we'll multiply all numbers from 0 to 10 by 10 and show the results.
The following code writes Toolinfy 5 times.
for(i=0; i<=10; i++){
var timesten = i*10;
document.write(i + " x " + "10" + " = " + timesten + "*<br/>");
}
This is how it would look:
Do-while loops
Of course we don't always know how often we want to execute a command/code block. Instead we want execute this block until a certain condition isn't true anymore. The syntax of do-while loops looks like this:
do{
//code block
} while(condition);
The following do-while loop will decrement the variable example
by 1 as long as its bigger than 0.
var example = 10;
do{
example -= 1;
document.write(example + "<br/>");
} while(example > 0);
Note that do-while loops are always executed at least once! This could lead to unwanted results.
While loops
While loops basically work the same way that do-while loops do. The only difference is that do-while loops are executed once and then the condition is checked, which means that they are always executed at least once. The condition in a while loop is checked before it's executed. If the condition isn't fulfilled the code block won't be executed at all.