Javascript.md

Javascript promise

    var id = $('#Id').val();
        var data = {
            'id': id
        };
        var serviceCall=function(){
        // Create a new Deferred object
        return new Promise(function(resolve, reject) {
            var options = {
                type: 'POST',
                url: '@Url.Action("Action", "Controller")',
                data: data,
                success: resolve,
                error: reject
            };

            $.ajax(options);
        });
        // Return the Deferred's Promise object
        }
        
        var successCallBack=function(result){
        if(result){
        // do the operation
        }
        };
        
        var errorCallBack=function(result, status, xhr, form){
        //Perform error handling
        };
        
        serviceCall().then(successCallBack, errorCallBack);

Internal working of Promise

         function Promise(executionFunction) {
           var state = ‘pending’; 
           var deferred = null; 
           var value;
           var resolveCallBacks=[];
            var rejectCallBacks=[];
           function resolve(value){
           state = ‘resolved’; 
            this.resolveCallBacks.forEach((nextFunction) => {
                  storedValue = nextFunction(value);
               });

           }
           function reject(error){
            state = ‘rejected’; 
          this.rejectCallBacks.forEach((nextFunction) => {
                  nextFunction(error);
               });
          }

           this.then = function(resolveCallBack,rejectCallBack){
           if(resolveCallBack){
           this.resolveCallBacks.push(resolveCallBack)
           }
            if(rejectCallBack){
           this.rejectCallBacks.push(rejectCallBack)
           }
           return this;
           }
           executionFunction(resolve, reject);
         }