JavaScript throwStatement

JavaScript 语句参考手册JavaScript Statement Reference

Example

This example checks the value of an input variable. If the value is wrong, an exception (err) is thrown.

The exception (err) is caught by the catch statement and a custom error message is 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>

Try it Yourself »

Definition and Usage

The throw statement throws an error.

When an error occurs, JavaScript stops executing and throws an error message.

The technical term for this situation is: JavaScript will throw an error.

throwThe statement creates custom errors.

The technical term is:throw an exception。

The exception can be a JavaScript string, number, boolean, or object:

throw "Too big"; // throw text
throw 500; // throw number

If you use throw withtry and catchtogether, you can control the program flow and generate custom error messages.

For more on JavaScript errors, read ourJavaScript ErrorsTutorial.

Browser Support

Statement
throw Yes Yes Yes Yes Yes

Syntax

throw expression;

Parameter Values

Parameter Description
expression Required. The exception to throw. Can be a string, number, boolean, or object.

Technical Details

JavaScript Version: 1.4

Related Pages

JavaScript Tutorial:JavaScript Errors

JavaScript Reference:JavaScript try/catch/finally Statement

JavaScript 语句参考手册JavaScript Statement Reference Other Extensions