JavaScript Global method: Boolean()
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The
JavaScript
Global
Boolean() method converts an
object to a Boolean representing the value of the object. If the parameter
value is omitted or is 0, -0, false, NaN, undefined, an empty string or the document.all DOM object then the
method evaluates to false. All
other parameter values (including the string “false”!) evaluate to true.
It
has the following syntax with the following parameters:
Boolean(x)
|
Parameter
|
Required / Optional
|
Description
|
|
x
|
Optional
|
Input parameter. If
missing, then returns false.
|
Note: it is easy to
confuse the primitive Boolean values true and false with the values of the
Boolean object. For example, any object whose value is not undefined or null
evaluates to true when passed to a conditional statement. So, the following
statements will result in the code being evaluated:
var x = new Boolean(false);
if (x) { code }
whereas it will not be
executed with the following statements:
var x = false;
if (x) { code }
The output of the global Boolean method can also be quite confusing
at it involves a type coercion that does not always behave intuitively.
EXAMPLE:
HTML USED IN THIS EXAMPLE:
<!DOCTYPE html>
<html> <!-- Copyright (c) Nematrian Limited 2018 -->
<head>
<style>
table,th,tr,td {border: 1px solid black; border-collapse :collapse;}
</style>
</head>
<body>
<table>
<tr>
<th>Example</th>
<th>Resulting value of <code>x</code></th>
</tr>
<tr>
<td><code id="Example"></code></td>
<td><code id="Result"></code></td>
</tr>
</table>
<script>
document.getElementById("Example").innerHTML =
'var x = Boolean("False");';
document.getElementById("Result").innerHTML =
Boolean("False");
</script>
</body>
</html>
|
FUNCTION THAT MAY ASSIST IN TESTING WHETHER FEATURE IS SUPPORTED:
function isSupportedJavaScriptMethodGlobalBoolean() {
return Boolean("Hello");
} |
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