hooks.js

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define(['jquery', 'elgg'], function ($, elgg) {
    // counter for tracking registration order
    var index = 0;
    
    // array that holds all hook registrations
    var hooks = {};
        
    function prepareHook(name, type) {
        hooks[name] = hooks[name] || [];
        hooks[name][type] = hooks[name][type] || [];
        
        hooks['all'] = hooks['all'] || [];
        hooks[name]['all'] = hooks[name]['all'] || [];
        hooks['all'][type] = hooks['all'][type] || [];
        hooks['all']['all'] = hooks['all']['all'] || [];
    }
    
    return {
        
        reset: function() {
            hooks = [];
        },

        register: function(name, type, handler, priority) {
            elgg.assertTypeOf('string', name);
            elgg.assertTypeOf('string', type);
            elgg.assertTypeOf('function', handler);
    
            if (!name || !type) {
                return false;
            }
    
            prepareHook(name, type);

            hooks[name][type].push({
                priority: priority,
                index: index++,
                handler: handler
            });
            
            return true;
        },
        
        trigger: function(name, type, params, value) {
            elgg.assertTypeOf('string', name);
            elgg.assertTypeOf('string', type);
        
            // default to null if unpassed
            value = (value != null) ? value : null;
        
            var registrations = [],
                push = Array.prototype.push;
        
            prepareHook(name, type);
        
            if (hooks[name][type].length) {
                if (name !== 'all' && type !== 'all') {
                    push.apply(registrations, hooks[name][type]);
                }
            }
            
            if (hooks['all'][type].length) {
                if (type !== 'all') {
                    push.apply(registrations, hooks['all'][type]);
                }
            }
            
            if (hooks[name]['all'].length) {
                if (name !== 'all') {
                    push.apply(registrations, hooks[name]['all']);
                }
            }
            
            if (hooks['all']['all'].length) {
                push.apply(registrations, hooks['all']['all']);
            }
        
            registrations.sort(function (a, b) {
                // priority first
                if (a.priority < b.priority) {
                    return -1;
                }
                
                if (a.priority > b.priority) {
                    return 1;
                }
        
                // then insertion order
                return (a.index < b.index) ? -1 : 1;
            });
        
            // only synchronous handlers
            $.each(registrations, function (i, registration) {
                var handler_return = registration.handler(name, type, params, value);
                if (handler_return != null) {
                    value = handler_return;
                }
            });
        
            return value;
        }
    };
});