Tutorials References Menu

JS Reference

JS by Category JS by Alphabet

JavaScript

JS Array JS Boolean JS Classes JS Date JS Error JS Global JS JSON JS Math JS Number JS Operators JS RegExp JS Statements JS String

HTML DOM

DOM Attributes DOM Document DOM Element DOM Events DOM Event Objects DOM HTMLCollection DOM Location DOM Navigator DOM Screen DOM Style
alignContent alignItems alignSelf animation animationDelay animationDirection animationDuration animationFillMode animationIterationCount animationName animationTimingFunction animationPlayState background backgroundAttachment backgroundColor backgroundImage backgroundPosition backgroundRepeat backgroundClip backgroundOrigin backgroundSize backfaceVisibility border borderBottom borderBottomColor borderBottomLeftRadius borderBottomRightRadius borderBottomStyle borderBottomWidth borderCollapse borderColor borderImage borderImageOutset borderImageRepeat borderImageSlice borderImageSource borderImageWidth borderLeft borderLeftColor borderLeftStyle borderLeftWidth borderRadius borderRight borderRightColor borderRightStyle borderRightWidth borderSpacing borderStyle borderTop borderTopColor borderTopLeftRadius borderTopRightRadius borderTopStyle borderTopWidth borderWidth bottom boxShadow boxSizing captionSide caretColor clear clip color columnCount columnFill columnGap columnRule columnRuleColor columnRuleStyle columnRuleWidth columns columnSpan columnWidth counterIncrement counterReset cursor direction display emptyCells filter flex flexBasis flexDirection flexFlow flexGrow flexShrink flexWrap cssFloat font fontFamily fontSize fontStyle fontVariant fontWeight fontSizeAdjust height isolation justifyContent left letterSpacing lineHeight listStyle listStyleImage listStylePosition listStyleType margin marginBottom marginLeft marginRight marginTop maxHeight maxWidth minHeight minWidth objectFit objectPosition opacity order orphans outline outlineColor outlineOffset outlineStyle outlineWidth overflow overflowX overflowY padding paddingBottom paddingLeft paddingRight paddingTop pageBreakAfter pageBreakBefore pageBreakInside perspective perspectiveOrigin position quotes resize right scrollBehavior tableLayout tabSize textAlign textAlignLast textDecoration textDecorationColor textDecorationLine textDecorationStyle textIndent textOverflow textShadow textTransform top transform transformOrigin transformStyle transition transitionProperty transitionDuration transitionTimingFunction transitionDelay unicodeBidi userSelect verticalAlign visibility width wordBreak wordSpacing wordWrap widows zIndex
DOM Window

Web APIs

API Console API Geolocation API History API Storage

HTML Objects

<a> <abbr> <address> <area> <article> <aside> <audio> <b> <base> <bdo> <blockquote> <body> <br> <button> <canvas> <caption> <cite> <code> <col> <colgroup> <datalist> <dd> <del> <details> <dfn> <dialog> <div> <dl> <dt> <em> <embed> <fieldset> <figcaption> <figure> <footer> <form> <head> <header> <h1> - <h6> <hr> <html> <i> <iframe> <img> <ins> <input> button <input> checkbox <input> color <input> date <input> datetime <input> datetime-local <input> email <input> file <input> hidden <input> image <input> month <input> number <input> password <input> radio <input> range <input> reset <input> search <input> submit <input> text <input> time <input> url <input> week <kbd> <label> <legend> <li> <link> <map> <mark> <menu> <menuitem> <meta> <meter> <nav> <object> <ol> <optgroup> <option> <output> <p> <param> <pre> <progress> <q> <s> <samp> <script> <section> <select> <small> <source> <span> <strong> <style> <sub> <summary> <sup> <table> <tbody> <td> <tfoot> <th> <thead> <tr> <textarea> <time> <title> <track> <u> <ul> <var> <video>

Other References

CSSStyleDeclaration JS Conversion


JavaScript try/catch/finally Statement


Example

In this example, we have made a typo in the code (in the try block).

The example is supposed to alert "Welcome guest!", but alert is misspelled.

The catch block catches the error, and executes a code to handle it:

<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>

<script>
try {
  adddlert("Welcome guest!");
}
catch(err) {
  document.getElementById("demo").innerHTML = err.message;
}
</script>

</body>
</html>
Try it Yourself »

More "Try it Yourself" examples below.


Definition and Usage

The try/catch/finally statement handles some or all of the errors that may occur in a block of code, while still running code.

Errors can be coding errors made by the programmer, errors due to wrong input, and other unforeseeable things.

The try statement allows you to define a block of code to be tested for errors while it is being executed.

The catch statement allows you to define a block of code to be executed, if an error occurs in the try block.

The finally statement lets you execute code, after try and catch, regardless of the result.

Note: The catch and finally statements are both optional, but you need to use one of them (if not both) while using the try statement.

Tip: When an error occurs, JavaScript will normally stop, and generate an error message. Use the throw statement to create a custom error (throw an exception). If you use throw together with try and catch, you can control program flow and generate custom error messages.

For more information about JavaScript errors, read out JavaScript Errors Tutorial.


Browser Support

Statement
try/catch/finally Yes Yes Yes Yes Yes

Syntax

try {
  tryCode - Block of code to try
}
catch(err) {
  catchCode - Block of code to handle errors
}
finally {
  finallyCode - Block of code to be executed regardless of the try / catch result
}

Parameter Values

Parameter Description
tryCode Required. Block of code to be tested for errors while it is being executed
err Required if used with catch. Specifies a local variable that refers to the error. The variable can refer to the Error object (contains information about the occurred error, like the message "'addlert' is not defined"). If the exception was created by the throw statement, the variable refers to the object specified in the throw statement (see "More Examples")
catchCode Optional. Block of code to be executed, if an error occurs in the try block. If no error occurs, this block of code is never executed
finallyCode Optional. Block of code to be executed regardless of the try / catch result


Technical Details

JavaScript Version: ECMAScript 3

More Examples

Example

This example examines input. 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 displayed:

<!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 »

Example

The finally statement lets you execute code, after try and catch, regardless of the result:

function myFunction()
  var message, x;
  message = document.getElementById("message");
  message.innerHTML = "";
  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 »

Related Pages

JavaScript Tutorial: JavaScript Errors

JavaScript Reference: JavaScript throw Statement