olegskl/invasive-kanji

/*jslint browser: true, unused: false */

/**
 * Assigns an event handler that is only executed once, then removed.
 * @param {Object}   subject      Observable subject.
 * @param {String}   eventName    Event name.
 * @param {Function} eventHandler Event handler.
 */
function addEventHandlerCalledOnce(subject, eventName, eventHandler) {
    'use strict';

    function eventHandlerCalledOnce() {
        // Unsubscribe self:
        subject.removeEventListener(eventName, eventHandlerCalledOnce);
        // This is going to happen only once:
        eventHandler();
    }

    // Validate subject for correctness to avoid cryptic error later:
    if (!subject || typeof subject !== 'object' ||
            typeof subject.addEventListener !== 'function') {
        throw new TypeError('Unable to assign a eventHandler called once.' +
                ' Invalid subject object.');
    }
    // Event handler must be a function:
    if (typeof eventHandler !== 'function') {
        throw new TypeError('Unable to assign a eventHandler called once.' +
                ' Callback must be a function.');
    }

    // It is now safe to add event eventHandler to the subject object:
    subject.addEventListener(eventName, eventHandlerCalledOnce);
}