EventBus implementation

Example:let bus = new EventBus();

bus.$on('event'.(data) = > {
            
    // out: test copy
    console.log(data);  
});

bus.$emit('event'.'Test copy');

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/** * Easy version event bus mechanism complete code */
class EventBus {
    constructor() {
        this.events = this.events || {};  //{key:Array}
    }

    / * * *@param {String} eventName 
     * @param {Function} callback 
     */
    $on(eventName, callback) {
        if (this.events[eventName]) {
            this.events[eventName].push(callback);
        } else {
            this.events[eventName] = [callback]; }}/ * * *@param {String} eventName 
     * @param {Function} callback 
     */
    $emit(eventName, data) {
        if (this.events[eventName]) {
            this.events[eventName].forEach(callback= >{ callback && callback(data); }); }}/ * * *@param {String} eventName 
     * @param {Function} callback 
     */
    $once(eventName, callback) {
        let _this = this;
        function handler(args) {
            callback.apply(_this, [args])
            _this.$off(eventName)
        }
        this.$on(eventName, handler)
    }

    / * * *@param {String} eventName 
     */
    $off(eventName) {

        if (eventName) {
            this.events[eventName] && (delete this.events[eventName]);
        } else {
            this.events = []; }}}Copy the code