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setTimeout function

setTimeout, a method of the window object, basically delays the execution of a function or statement until the specified time has passed. The basic syntax of this function is:

setTimeout("expression", delaytime)

"expression" is the function/statement you want delayed, and delaytime is the delay time, in milliseconds.

For example, this will output "Three seconds have gone!" after 3 seconds.


document.three.hi.value=""
//simply clears the text box
function talk(){
setTimeout("document.three.hi.value='Three seconds have gone!'",3000)
}

<form name="three">
<input type="text" size="28">
<input type="button" value="Start" onClick="talk()">
</form>

Let's do a example that, by placing the setTimeout in a special position, continuously writes to a box, incrementally itself every second.


var c=0
document.go.timer.value=""
function count()
{
document.go.timer.value=c
c=c+1
setTimeout("count()",1000)
}

<form name="go">
<input type="text" name="timer" size="12">
<input type="button" value="Start" onClick="count()">
</form>
  • A very important point is that the setTimeout method executes count() after one second, but look at the place where setTimeout is placed-inside count()! This will execute everything within function count(), including setTimeout itself, every one second. Basically, this forces the function to loop back and start at the beginning each time it encounters this method. If you don't get it, study it a little harder-you'll see it!
  • The above function will run forever, until you reload or leave. This is exactly the function we need to create a clock, since we need a function that will continuously update itself. This function is so important, because whenever you write something that needs continuous refreshment, all you have to do is put a setTimeout function inside another function and call it. Now, a little thought will tell us that we can control this function, if we want to, so that it does not run forever- namely, by putting it in an if-else-statement. Note that to get "1" second, we used "1000". (1 millisecond*1000) equals 1 second.

Using setTimeout, we can implement a live clock. Ok, now that we have all the tools, lets do just that.

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