index.md

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title: boolean
slug: Web/XPath/Functions/boolean

---

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The boolean function evaluates an expression and returns true or false.

Syntax

boolean( expression )

Arguments

• expression

  • : The expression to be evaluated. The expression can refer to numbers and node-sets as well as booleans.

Returns

Boolean true or false after evaluating expression.

Notes

• A number evaluates to false if it is positive or negative zero or NaN. Otherwise, it evaluates true.

• A node-set evaluates to true if it is non-empty.

• A string evaluates to false if it an empty string. Otherwise, it evaluates to true.

• An object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type.

Defined

XPath 1.0 4.3

Gecko support

Supported.