JavaScript syntax: Difference between revisions

Revision as of 23:24, 24 April 2016

Revision as of 14:26, 27 April 2016

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===Boolean===

[[JavaScript]] provides a [[Boolean data type]] with {{mono|true}} and {{mono|false}} literals. The typeof operator returns the string {{mono|"boolean"}} for these [[primitive types]]. When used in a logical context, {{mono|0}}, {{mono|-0}}, {{mono|null}}, {{mono|NaN}}, {{mono|undefined}}, and the empty string ({{mono|""}}) evaluate as {{mono|false}} due to automatic [[type coercion]]. The [[complement (set theory)|complement]] evaluates as {{mono|true}}, including the strings {{mono|"0"}}, {{mono|"false"}} and any object (except {{mono|null}}). Automatic type coercion by the equality comparison operators (<code>==</code> and <code>!=</code>) can be avoided by using the type checked comparison operators, (<code>===</code> and <code>!==</code>).

When type conversion is required, JavaScript converts {{mono|Boolean}}, {{mono|Number}}, {{mono|String}}, or {{mono|Object}} operands as follows:<ref>{{cite web | url=https://developer.mozilla.org/en/JavaScript/Reference/Operators/Comparison_Operators | title=Comparison Operators - MDC Doc Center | publisher=Mozilla | date=5 August 2010 | accessdate=5 March 2011}}</ref>

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alert( 1 ? true : false); // true.... only ±0 and NaN are “falsy” numbers

alert("0" ? true : false); // true.... only the empty string is “falsy”

alert(Boolean({})); // true.... all objects are “truthy” except null

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