javascript - Accesing the object's property form a nested function -

this question has answer here:

• how access correct `this` inside callback? 5 answers

here java script code.

var fiat = {      make: "fiat",     model: "500",     year: 1957,      color: "medium blue",     passengers: 2,     convertible: false,     mileage: 88000,     fuel: 0,     started: false,      start: function() {         if (this.fuel == 0) {             console.log("the car on empty, fill before starting!");         } else {             this.started = true;         }     },      stop: function() {         this.started = false;     },       drive: function() {         function update(){             this.fuel-=-1;          }           if (this.started) {             if (this.fuel > 0) {                 console.log(this.make + " " +                       this.model + " goes zoom zoom!");                 update();             } else {                 console.log("uh oh, out of fuel.");                 this.stop();             }          } else {             console.log("you need start engine first.");         }     },      addfuel: function(amount) {         this.fuel = this.fuel + amount;     } }; 

i want update fuel invoking helper function "update()" nested inside property function "drive". checked in console seems can't access variables this.fuel property since prints "nan".

the question how access objects property "update()" helper nested inside "drive" property function can make changes "this.fuel". thanks.

use this

drive: function() {          var that= this;          function update(){              that.fuel-=-1;          }