JavaScript try...catch statement

　JavaScript Statements and Variable Declarations

try ... catchThe statement marks the block of statements to be tried and specifies the response when an exception (error) is thrown.

The try statement consists of a try block that contains one or more statements. {} must always be used for a single statement.

There must be at least one catch clause or finally clause. This provides three forms for the try statement:

• try...catch

• try...finally

• try...catch...finally

UsetryThe statement can define a code block that will be tested for errors during execution.

catchThe statement allows you to define a code block that will be executed if an error occurs in the try block.

finallyIn the declaration, the code you can execute after try and catch, regardless of the result.

Note: Both catch and finally statements are optional, but when using the try statement, you must use one of them (if you cannot use both).

UsethrowThe statement creates a custom error (throws an exception). If you willthrowWhen used with try and catch, it allows you to specify the program flow and generate custom error messages (see the 'More Examples' below).

You can find more information about ourJavaScript exception tutorialLearn more about exceptions in the

Syntax:

try {
　　　//try_statements-The statements to be tried
}
catch(err) {
　　　//catch_statements-Error handling statements
}
finally {
　　//finally_statements-Regardless of the try　/　Statements to be executed regardless of the result of the catch
}

try {
　　　aaalert("Hello world");
}
catch(err) {
　　　document.getElementById("result").innerHTML = err;
}

Browser compatibility

All browsers fully support the try ... catch statement:

Parameter value

Technical details

More examples

InfinallyIn the declaration, you can execute code, after try and catch, regardless of the result:

try {
　　　aaalert("Hello world");
}
catch(err) {
　　　document.getElementById("result").innerHTML = err;
}
finally {
　　　document.getElementById("result").innerHTML　+= "<h3>Finally statement executed</h3>";
}

catchandfinallyStatements are optional, but when using the try statement, you need to use one of them (if you cannot use them together):

try {
　　　aaalert("Hello world");
}
finally {
　　　document.getElementById("result").innerHTML = "Final execution statement";
}

UsethrowStatement creates a custom error (raises an exception):

function getRectArea(width,　height) {
　　　if (isNaN(width) || isNaN(height)) {
　　throw "The parameter is not a number!";
　　　}
}
try {
　　　getRectArea(5,　'Z');
}
catch(err) {
　　　document.getElementById('para').innerHTML = err;
}

Check the input, if the value is incorrect, then raise an exception (err).catchCatch exceptions (err) and display custom error messages:

var x = document.querySelector("input").value;
try {
　　　if(x == "")    throw "is Empty";
　　　)    throw "Not a Number";
　　　if(x >　10)    throw "too High";
　　　if(x <　5)throw "too Low";
}
catch(err) {
　　　document.getElementById("para").innerHTML = "Input"　+　err;
}

You can also check out

JavaScript Tutorial:JavaScript Exceptions

JavaScript Reference:JavaScript Error Object

JavaScript Reference:JavaScript throw Statement

　JavaScript Statements and Variable Declarations