javascript passing a function in a class that needs another function from that class object - Stack Overflow

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I am passing a function in a class or var object as an argument to another function. The function that takes in the function from the class executes that function. It would work fine, however the function of the class calls another function from the class. The console outputs the error that the function being called in the class function is undefined.

The following might illustrate a bit better

//the class variable in someClass.js
function(params...){
  getSomethingInClass: function(){
     // return some variable
  }

  functionThatIsPassed: function(arg){
    var theCalledFunction = getSomethingInClass();
    //do something with theCalledFunction
  }
}

//SOME WHERE ELSE in another function in another file
OtherFunction: function(){
//someClass is a variable being used here
  FunctionThatTakesFunction(this.someClassVar.functionThatIsPassed);
}


//FunctionThatTakesFunction is implemented in another file
FunctionThatTakesFunction(callbackFun){
  callbackFun(someArg);
}

The above will work if I change it to pass the entire object someClass object. That is bad programming practice to pass the object because FunctionThatTakesFunction needs to know the functions of its argument For example

//THIS WORKS!
//other stuff is same 

//SOME WHERE ELSE in another function in another file
OtherFunction: function(){
//someClass is a variable being used here
  FunctionThatTakesFunction(this.someClassVar);
}


//FunctionThatTakesFunction is implemented in another file
FunctionThatTakesFunction(object){
  object.functionThatIsPassed(someArg);
}

I am passing a function in a class or var object as an argument to another function. The function that takes in the function from the class executes that function. It would work fine, however the function of the class calls another function from the class. The console outputs the error that the function being called in the class function is undefined.

The following might illustrate a bit better

//the class variable in someClass.js
function(params...){
  getSomethingInClass: function(){
     // return some variable
  }

  functionThatIsPassed: function(arg){
    var theCalledFunction = getSomethingInClass();
    //do something with theCalledFunction
  }
}

//SOME WHERE ELSE in another function in another file
OtherFunction: function(){
//someClass is a variable being used here
  FunctionThatTakesFunction(this.someClassVar.functionThatIsPassed);
}


//FunctionThatTakesFunction is implemented in another file
FunctionThatTakesFunction(callbackFun){
  callbackFun(someArg);
}

The above will work if I change it to pass the entire object someClass object. That is bad programming practice to pass the object because FunctionThatTakesFunction needs to know the functions of its argument For example

//THIS WORKS!
//other stuff is same 

//SOME WHERE ELSE in another function in another file
OtherFunction: function(){
//someClass is a variable being used here
  FunctionThatTakesFunction(this.someClassVar);
}


//FunctionThatTakesFunction is implemented in another file
FunctionThatTakesFunction(object){
  object.functionThatIsPassed(someArg);
}

• javascript
• function
• parameter-passing

Share Improve this question Follow asked Jul 31, 2013 at 20:10 SakibSakib 1,54366 gold badges2727 silver badges4343 bronze badges 3

• 1 And what is your question? – Jackson Ray Hamilton Commented Jul 31, 2013 at 20:13
• I want to just pass the function from the class and call it instead of passing the class object and calling the function after that – Sakib Commented Jul 31, 2013 at 20:26
• FunctionThatTakesFunction(this.someClassVar.bind(this)); – dandavis Commented Jul 31, 2013 at 21:09

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 2

Here are some examples of passing a function into another function: (Fiddle here: http://jsfiddle/FvyUQ/4/)

function Cat() {
  this.myMeow = 'Mrrow';

  this.scratch = function() {
    console.log('Scritchey-scratch.');
  }
}

Cat.prototype.meow = function() {
  console.log(this.myMeow);
}

Cat.prototype.jump = function() {
  console.log('The cat jumped and said ' + this.myMeow + '!');
}

function test(fn) {
  fn();
}

function callPrototype(fn, context) {
  fn.call(context);
}

var myCat = new Cat();

test(myCat.scratch);
test(myCat.meow);
test(myCat.jump);
test(Cat.prototype.jump);
callPrototype(Cat.prototype.jump, myCat);

I use Closures:

class Sample() {
    constructor() {
        this.id = 'Sample';
    }

    method(text) {
        console.log(this.id + text)
    }

    getMethod() {
        const ref = this;
        return function(text) {
            ref.method(text);
        }
    }
}

Elsewhere:

someFunc() {
    const sample = new Sample();
    useFunc(sample.getMethod());
}

useFunc(func) {
    func('HI');
}

Output: SampleHI

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