Example
This example has a typo in the
try block
. Alert is misspelled.
The
catch block
catches the error and executes the code to handle it:
<p id="demo"></p>
<script>
try {
adddlert("Welcome guest!");
}
catch(err) {
document.getElementById("demo").innerHTML = err.message;
}
</script>
Try it Yourself »
More examples below.
Definition and Usage
When an
error
occurs, JavaScript will
stop
and generate an error message.
The technical term for this is is: JavaScript
throws an exception
.
JavaScript creates an
Error object
with two properties:
name
and
message
.
The
try...catch...finally
statements combo handles errors without stopping JavaScript.
The
try
statement defines the code block to run (to try).
The
catch
statement defines a code block to handle any error.
The
finally
statement defines a code block to run regardless of the result.
The
throw
statement defines a custom error.
Both
catch
and
finally
are optional, but you must use one of them.
Using
throw
with
try
and
catch
, lets you control program flow and generate
custom error messages.
See Also:
The JavaScript throw
JavaScript Error Object
JavaScript Errors Tutorial
catchCode -
Code block to handle errors
}
finally {
finallyCode - Code block to be executed regardless of the try result
}
Parameters
Parameter
Description
tryCode
Required.
Code block to be tested while executing.
A local reference to the error object.
catchCode
Optional.
Code block to execute if an error occurs.
finallyCode
Optional.
Code block to execute regardless of the try result
<p>Please input a number between
5 and 10:</p>
<input id="demo" type="text">
<button type="button"
onclick="myFunction()">Test Input</button>
<p id="message"></p>
<script>
function myFunction() {
const message =
document.getElementById("message");
message.innerHTML = "";
let x =
document.getElementById("demo").value;
try {
if(x == "") throw "is Empty";
if(isNaN(x)) throw "not a number";
if(x > 10) throw "too high";
if(x < 5) throw "too low";
}
catch(err) {
message.innerHTML =
"Input " + err;
}
}
</script>
Try it Yourself »
The
finally
statement executes code, after regardless of the try result:
function myFunction()
const message =
document.getElementById("message");
message.innerHTML = "";
let x =
document.getElementById("demo").value;
try {
if(x == "") throw "Empty";
if(isNaN(x))
throw "Not a number";
if(x >
10) throw "Too high";
if(x <
5) throw "Too low";
}
catch(err)
{
message.innerHTML = "Error: " +
err + ".";
}
finally {
document.getElementById("demo").value = "";
Try it Yourself »
Browser Support
try...catch
is an ECMAScript3 (ES3) feature.
ES3 (JavaScript 1999) is fully supported in all browsers:
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