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JavaScript Reference

JavaScript

JS String JS Number JS Operators JS Statements JS Math JS Date JS Array JS Boolean JS RegExp JS Global JS Conversion

Browser BOM

Window Navigator Screen History Location

HTML DOM

DOM Document DOM Elements DOM Attributes DOM Events DOM Style

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> <keygen> <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> <td> <th> <tr> <textarea> <time> <title> <track> <u> <ul> <var> <video>

Other Objects

CSSStyleDeclaration

JavaScript undefined Property

Function Reference JavaScript Global Functions

Example

Test if a variable is undefined:

var x;

if (x === undefined) {
txt = "x is undefined";
} else {
txt = "x is defined";
}

The result of txt will be:

x is undefined

Try it yourself »

More "Try it Yourself" examples below.

Definition and Usage

The undefined property indicates that a variable has not been assigned a value.

Browser Support

Property
undefined	Yes	Yes	Yes	Yes	Yes

Technical Details

JavaScript Version:	1.3

More Examples

Example

Test if variables are undefined:

var t1 = "myVar";               // defined
var t2;                         // undefined

if (t1 === undefined) {
    txt1 = "t1 is undefined";
} else {
    txt1 = "t1 is defined";
}

if (t2 === undefined) {
    txt2 = "t2 is undefined";
} else {
    txt2 = "t2 is defined";
}

txt = txt1 + "<br>" + txt2;

The result of txt will be:

t1 is defined
t2 is undefined

Try it yourself »

Function Reference

JavaScript Global Functions

COLOR PICKER

colorpicker

LEARN MORE:

Color Converter
Google Maps
Animated Buttons
Modal Boxes
Modal Images
Tooltips
Loaders
JS Animations
Progress Bars
Dropdowns
Slideshow
Side Navigation
HTML Includes
Color Palettes

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