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Proxy

Proxy object.

Installation

npm install @stdlib/proxy-ctor

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var Proxy = require( '@stdlib/proxy-ctor' );

Proxy( target, handlers )

Returns a proxy object implementing custom behavior for specified object operations.

function get( target, property ) {
    return target[ property ] * 2.0;
}

var handlers = {
    'get': get
};

var p = new Proxy( {}, handlers );

p.a = 3.14;

var v = p.a;
// returns 6.28

A handlers argument should be an object whose properties are functions (called "traps") which define the behavior of the proxy when performing operations. The following traps are supported:

• getPrototypeOf( target )

  • Trap for Object.getPrototypeOf(). Can be used to intercept the instanceof operator. The method must return an object or null.

• setPrototypeOf( target, prototype )

  • Trap for Object.setPrototypeOf(). The method must return a boolean indicating if the prototype was successfully set.

• isExtensible( target )

  • Trap for Object.isExtensible(). The method must return a boolean.

• preventExtensions( target )

  • Trap for Object.preventExtensions(). The method must return a boolean.

• getOwnPropertyDescriptor( target, property )

  • Trap for Object.getOwnPropertyDescriptor(). The method must return an object or undefined.

• defineProperty( target, property, descriptor )

  • Trap for Object.defineProperty(). The method must return a boolean indicating whether the operation succeeded.

• has( target, property )

  • Trap for the in operator. The method must return a boolean.

• get( target, property, receiver )

  • Trap for retrieving property values. The method can return any value.

• set( target, property, value, receiver )

  • Trap for setting property values. The method should return a boolean indicating whether assignment succeeded.

• deleteProperty( target, property )

  • Trap for the delete operator. The method must return a boolean indicating whether operation succeeded.

• ownKeys( target )

  • Trap for Object.keys, Object.getOwnPropertyNames(), and Object.getOwnPropertySymbols(). The method must return an enumerable object.

• apply( target, thisArg, argumentsList )

  • Trap for a function call. The method can return any value.

• construct( target, argumentsList, newTarget )

  • Trap for the new operator. The method must return an object.

All traps are optional. If a trap is not defined, the default behavior is to forward the operation to the target.

Examples

var Float64Array = require( '@stdlib/array-float64' );
var Proxy = require( '@stdlib/proxy-ctor' );

var handlers;
var arr;
var p;
var i;

// Create a new typed array:
arr = new Float64Array( 10 );
for ( i = 0; i < arr.length; i++ ) {
    arr[ i ] = i;
}

// Define a "trap" when retrieving property values:
function get( obj, prop ) {
    if ( prop === 'length' ) {
        return obj.length;
    }
    return obj[ prop ] * 2.0;
}

// Define the proxy handlers:
handlers = {
    'get': get
};

// Create a proxy:
p = new Proxy( arr, handlers );

// Access array values...
for ( i = 0; i < p.length; i++ ) {
    console.log( 'arr[%d] = %d', i, p[ i ] );
}

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.