method chaining failed in javascript

Question

I'm trying to train myself to write chaining function but got error of

Cannot read property 'minus' of undefined(…)

What's wrong with my code?

 var math = function(){ var result = 0; var add = function(param){ result += param; }; var minus = function(param){ result -= param; }; var print = function(){ console.log(result) }; return {add:add, minus: minus, print:print}; } var calculator = math(); var result = calculator.add(5).minus(1).print(); console.log(result) 

Answer 1

You need to return the object ( this ) in this case, to "chain" like you are expecting

You print() also doesn't return anything so result is always undefined.

 var math = function(){ var result = 0; var add = function(param){ result += param; return this; }; var minus = function(param){ result -= param; return this; }; var print = function(){ console.log('result: ' + result); // print doesnt return anything, it needs to if you want to assign anything by calling it return result; }; return {add:add, minus: minus, print:print}; } var calculator = math(); var result = calculator.add(5).minus(1).print(); console.log(result) 

Answer 2

You can also store a reference to the object returned.

 var math = function() { var result = 0; var add = function(param) { result += param; return math; }; var minus = function(param) { result -= param; return math; }; var print = function() { console.log(result) }; var math = { add: add, minus: minus, print: print }; return math; } var calculator = math(); calculator.add(5).minus(1).print();