Why am I getting undefined error in my array?

[Jen O]

<script>
		window.onload=myday;
			
			function myday(){
				
			var day=new Array("sunday","monday","tuesday","wednesday","thursday","friday","saturday");
			
			var d=new Date();
			theDay=d.getDay();
			
			for (i=0;i<=day.length;i++)
			{
					if (i!=theDay)
				{
				
				document.write("today is not " + day[i]);
				document.write("<br />");}
				
				else
				{
					document.write("today is " + day[i]);
					document.write("<br />");}
			}
			}
			
			
</script>

[Dormilich]

because you use document.write( ).

if you call document.write( ) after the page finished loading (i.e. when onload is triggered) document.write( ) erases* the current document (completely) and writes the document anew. at that point all your JavaScript has been erased and thus your function is not defined.


* - it does that by implicitly calling document.open()

[Jen O]

How do you recommend I get around this? I have this example from my book(below), and it uses the onload with document.write. I believe this is why I am confused.

<script type="text/javascript">
	window.onload=initAll;

	function initAll(){
	var allmonths = new Array ("january","february","march","april","may","june","july","august","september","october","november","december")
	var birthmonth = prompt("what is your birth month?","");
	for(i=0;i<allmonths.length;i++){
		if (allmonths[i]==birthmonth){
			document.write("<strong>"+(i+1)+". "+allmonths[i]+" is your birth month!"+"</strong></br >");
			alert("Hooray "+allmonths[i]+" is your birth month!");
		} else{
			document.write((i+1)+". "+allmonths[i]+" is "+"<strong>"+"NOT"+"</strong>"+" your birth month!"+"</br >");
		}
	}

}
	</script>

[JKing]

It's a very small error. In your for loop you have for (i=0;i<=day.len gth;i++)

but if you compare this to your example for(i=0;i<allmo nths.length;i++ ) you will notice the operator <= should be <.

You want your loop to terminate before 'i' is equal to the length. This is because arrays start at 0. If you have an array with length of 5 you would have indexes 0,1,2,3,4 but not 5.