Need some JavaScript definitions

Hi Everybody!

Good day
I like to know some JavaScript definitions are following:

try_catch_statement:

<html>
<head>
<script type="text/javascript">
var txt="";
function message()
{
try
  {
  adddlert("Welcome guest!");
  }
catch(err)
  {
  txt="There was an error on this page.\
\
";
  txt+="Error description: " + err.description + "\
\
";
  txt+="Click OK to continue.\
\
";
  alert(txt);
  }
}
</script>
</head>

<body>
<input type="button" value="View message" onClick="message()" />
</body>

</html>

Please see the codes above and give me the following answer:

#  What is “txt”? Why I should use this?
#  What is “There was an error on this page.\
\
”? What is .\
\
?
# What is “txt+="Error description: " + err.description + "\
\
";” here? I mean
 txt+,
 Error description:,
 err.description and
 "\
\
"?
# What is “onClick="message()” as well?



throw_statement:


```html4strict
<html>
<body>
<script type="text/javascript">
var x=prompt("Enter a number between 0 and 10:","");
try
{
if(x>10)
  {
  throw "Err1";
  }
else if(x<0)
  {
  throw "Err2";
  }
else if(isNaN(x))
  {
  throw "Err3";
  }
}
catch(er)
{
if(er=="Err1")
  {
  alert("Error! The value is too high");
  }
if(er=="Err2")
  {
  alert("Error! The value is too low");
  }
if(er=="Err3")
  {
  alert("Error! The value is not a number");
  }
}
</script>
</body>
</html>

What is “else if(isNaN(x))”? Why I should use it?

No more, I am waiting for your kind response.

Thank you.:slight_smile:

Hi,

A string. It contains an error message which is passed to alert() in the case that the first function cannot be executed successfully.

Two newline characters.

An example of string concatenation.

An inline event handler, which executes a function (“message”) in the case that the user clicks on the element it is bound to.

A function which checks to see if “x” is Not a Number.

Hope that helps.

Might I also suggest that you check out a couple of beginner JavaScript tutorials, such as this one.