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Global Functions
Global, or top level functions, are functions in JavaScript that are
independent of any particular object.
Global functions
Note:
"[]" surrounding a parameter below means the parameter is optional.
| Operator |
Description |
| parseInt(x, [radix]) |
Parses any string "x" and returns the
first valid number (integer) it encounters. If the first character
in the string is not a number, white spaces, or a leading minus
sign, parseInt() returns NaN instead. You can test for NaN using the isNaN() function below.
parseInt() supports an optional 2nd "radix" parameter to specify the base of the number to be parsed (valid
range is 2-36). Entering "10"
would parse the number in the familiar decimal system, while "16"
would be hexadecimal. Without this parameter present, parseInt()
assumes any number that begins with "0x" to be radix 16, "0" to be
radix 8, and any other number to be radix 10.
Examples:
parseInt("3 chances") //returns 3
parseInt(" 5 alive") //returns 5
parseInt("I have 3 computers") //returns NaN
parseInt("17", 8) //returns 15 |
| parseFloat(x) |
Parses any string "x" and returns the
first valid floating point number it encounters. Use this function
to extract numbers with decimals, for example. If the first
character in the string is not a number, white spaces, or a leading
minus sign, parseFloat() returns NaN instead. You can test for NaN using the isNaN() function below.
Example:
parseFloat("-3.98 points") //returns -3.98 |
| isNaN(x) |
isNaN() checks its parameter "x" to see
if it's the value "NaN" (not a number)- an illegal number. The
function returns true if "x" is NaN, and false if not. A common
example of NaN is 0 divided by 0. This function is required to
detect NaN, as using equality operators (== or ===) won't do. |
| isFinite(x) |
Determines whether a number is finite.
Returns false if x is +infinity, -infinity, or NaN. JavaScript 1.3
statement. |
| eval(s) |
Evaluates the string ("s") and returns
the results of the evaluation (if available). Eval() allows you to dynamically
construct a JavaScript statement or expression. Examples:
eval("8+3+1") //returns 12
eval("alert(Math.random())") //alerts Math.random() |
| escape(s) |
Accepts a string "s" and returns its
encoded version. Original string isn't modified. All characters
within the string that are non-alphanumeric nor one of the
characters @ * - + . / are encoded. The escape() function is often
used to encode cookie values before they're stored into a cookie
(such as a URL). Note that escape() has been deprecated in
ECMAScript 3.0 in favor of encodeURI(). The later is
supported in JavaScript 1.5 and up, while the former indefinitely
(though formally deprecated). Example:
escape("JavaScript Kit") //returns
"JavaScript%20Kit" |
| unescape(s) |
Unescapes an encoded string "s"
previously encoded by escape(). Note that escape() has been
deprecated in ECMAScript 3.0 in favor of decodeURI(). The
later is supported in JavaScript 1.5 and up, while the former
indefinitely (though formally deprecated). |
alert(), confirm()
and prompt()
These three methods of the Window object are often confused as top-level functions
(since the "window" prefix is typically omitted when using them), so we'll
listing them here just for your convenience. You can also see an explanation of
alert(), confirm() and prompt() on the Windows object page.
| methods |
Description |
| alert(msg) |
Displays an Alert dialog
box with the desired message and OK button. |
| confirm(msg) |
Displays a Confirm dialog
box with the specified message and OK and Cancel buttons.
Example(s) |
| prompt(msg, [input]) |
Displays a Prompt dialog
box with a message. Optional "input" argument allows you to specify
the default input (response) that gets entered into the dialog box.
Set "input" to "" to create a blank input field.
Example(s) |
Examples
confirm(msg)
var yourstate=window.confirm("Are you sure you are ok?")
if (yourstate) //Boolean variable. Sets to true if user pressed "OK" versus
"Cancel."
window.alert("Good!")
prompt(msg, [input])
var thename=window.prompt("please enter your name")
window.alert(thename)
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