define([
        './addToArray',
        '../../Core/defined'
    ], function(
        addToArray,
        defined) {
    'use strict';

    /**
     * Adds an extension to gltf.extensionsUsed if it does not already exist.
     * Initializes extensionsUsed if it is not defined.
     *
     * @param {Object} gltf A javascript object containing a glTF asset.
     * @param {String} extension The extension to add.
     *
     * @private
     */
    function addExtensionsUsed(gltf, extension) {
        var extensionsUsed = gltf.extensionsUsed;
        if (!defined(extensionsUsed)) {
            extensionsUsed = [];
            gltf.extensionsUsed = extensionsUsed;
        }
        addToArray(extensionsUsed, extension, true);
    }

    return addExtensionsUsed;
});