# Namespace Resolvers
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The methods on the [XPathEvaluator](XPathEvaluator.md) type can optionally take a namespace resolver to resolve
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namespace references in the XPath expression being evaluated.
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There are three ways to specify a namespace resolver and you can use any one of them depending on which is
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most suited to your particular situation.
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## Namespace Resolver Type 1: Plain object
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A plain object with namespace prefixes as the keys and namespace URIs as the values:
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Example usage:
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```js
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var evaluator = xpath.parse('/bk:book/hp:characters');
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var characters = evaluator.select({
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node: myBookNode,
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namespaces: {
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'bk': 'http://sample.org/books/',
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'hp': 'http://sample.org/harrypotter/'
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}
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});
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```
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## Namespace Resolver Type 2: Function
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A function that takes a namespace prefix as a parameter and returns the corresponding namespace URI.
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Example usage:
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```js
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var evaluator = xpath.parse('/bk:book/hp:characters');
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var characters = evaluator.select({
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node: myBookNode,
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namespaces: function (prefix) {
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if (prefix === 'bk') {
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return 'http://sample.org/books/';
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}
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if (prefix === 'hp') {
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return 'http://sample.org/books/';
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}
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}
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});
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```
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## Namespace Resolver Type 3: Object with `getNamespace` method
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An object with a method named `getNamespace` that works in the same way as the function-based namespace resolver
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described above.
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Example usage:
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```js
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var evaluator = xpath.parse('/bk:book/hp:characters');
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var characters = evaluator.select({
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node: myBookNode,
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namespaces: {
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getNamespace: function (prefix) {
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if (prefix === 'bk') {
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return 'http://sample.org/books/';
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}
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if (prefix === 'hp') {
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return 'http://sample.org/books/';
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}
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}
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}
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});
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```
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