JavaScript throw
Statement
JavaScript Statements Reference Manual
Example
This example checks the value of the input variable. If the value is incorrect, an exception (err) is thrown.
The exception (err) is caught by the catch statement and custom error messages are output:
<!DOCTYPE html><html><body><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() { var message, x;
message =
document.getElementById("message"); message.innerHTML = "";
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></body></html>
Definition and Usage
The throw
statement throws an error.
When an error occurs, JavaScript stops execution and throws an error message.
The technical term for this situation is: JavaScript will throw an error.
The throw statement creates a custom error.
The technical term is: throw an exception.
The exception can be a JavaScript string, number, boolean, or object:
If used together with try and catch, you can control program flow and generate custom error messages.
For more JavaScript error information, please read our JavaScript Errors tutorial.
Browser Support
Statement | Chrome | Edge | Firefox | Safari | Opera |
---|---|---|---|---|---|
throw | Yes | Yes | Yes | Yes | Yes |
Syntax
Parameter Values
Parameter | Description |
---|---|
expression | Required. The exception to be thrown. It can be a string, number, boolean, or object. |
Technical Details
| JavaScript Version: | 1.4 | | --- | --- |
Related Pages
JavaScript Tutorial: JavaScript Errors
JavaScript Reference Manual: JavaScript try/catch/finally Statement