Javascript method is not a function

Question

function makeGroup(param) {
  this.group = param;
}

duplicateEmployee.makeGroup(index2);

Doing a simple duplicateEmployee.group = index2 doesn't work. Trying a method says "makeGroup is not a function."

Here's the full code for reference.

var someVar = [];
vm.contacts = ContactsService.query(employees => {
  employees.forEach(employee => {
    employee.groups.forEach((groupMembership, index2) => {
      // getEmployee() works...
      function getEmployee(param) {
        return param;
      }

      // "makeGroup is not a function"
      function makeGroup(param) {
        this.group = param;
      }

      var duplicateEmployee = getEmployee(employee);
      if (groupMembership) {
        duplicateEmployee.makeGroup(index2); // this breaks it. Says makeGroup is not a function
        console.log(groupMembership, index2); // index2 is working... that's the group number
        someVar.push(duplicateEmployee);
      }
    });
  });
});
vm.contacts = someVar;

Tried this and it doesn't work

      function makeGroup(param1, param2) { // console.log(param2) === undefined
        console.log(param1); // group number... not the employee (still useful)
        console.log(this); // 'this' is the employee, so lets try this.group
        this.group = param1; // still overwriting the variable
      }

      makeGroup.call(duplicateEmployee, index2)

duplicateEmployee is just a variable that has whichever value param has, it doesn't have a function called makeGroup — Lixus
– Lixus, Commented May 30, 2017 at 22:28
That is because your employee object has no makeGroup function. — Travis J
– Travis J, Commented May 30, 2017 at 22:28
so instead of function makeGroup it should be function duplicateEmployee.makeGroup (param) {}? — Tyler L
– Tyler L, Commented May 30, 2017 at 22:29
@TravisJ that's why I'm confused with methods. Normally functions just work, and I'm not sure the difference. — Tyler L
– Tyler L, Commented May 30, 2017 at 22:30
No, for that to work you'd have to make an Employee kind of class, add makeGroup to it's prototype, create a new class in your code, and then call that function. Also I don't get the point of creating those two functions only available in your forEach scope. — Lixus
– Lixus, Commented May 30, 2017 at 22:31

glhrmv · Accepted Answer · 2017-05-30 22:37:07Z

2

You're calling a method makeGroup of a duplicateEmployee object. This object does not have this method in it. You can either add it to its prototype or just change makeGroup so that it's a function that takes in the employee and the param, and it'd be something like so.

function makeGroup(employee, param) {
  employee.group = param;
}

The reason getEmployee works is because you're calling it from the global context, and not from a duplicateEmployee context like you're doing with makeGroup.

answered May 30, 2017 at 22:37

glhrmv

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2 Comments

Tyler L Over a year ago

Thank you. employee.group keeps getting overwritten when I try this. It would be the same as saying duplicateEmployee.group = index2

glhrmv Over a year ago

That's because your duplicateEmployee isn't actually getting a copy of the employee you want, it's getting a reference to it. So whenever you change duplicateEmployee you're also changing employee. Can you tell me if the problem is fixed if you do return Object.assign({}, param) instead of return param in getEmployee?

Daniel Taub · Accepted Answer · 2017-05-30 22:34:40Z

1

duplicateEmployee.makeGroup(index2); can't be called from the employee because it's not a member of that.
You can just call it like that makeGroup(index2)

answered May 30, 2017 at 22:34

Daniel Taub

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6 Comments

dime2lo Over a year ago

I have my doubts if this is going to work once inside makeGroup it is using "this". Maybe he could pass an employee as a parameter or invoke through makeGroup.call(duplicateEmployee, index2)

Tyler L Over a year ago

So should I create a whole new method to construct the employee for this one? Something like this w3schools.com/js/tryit.asp?filename=tryjs_create_object3

Tyler L Over a year ago

@dime2lo "CreateListFromArrayLike called on non-object" when I try makeGroup.apply(duplicateEmployee, index2) and function makeGroup(param1, param2) { param1.group = param; }

dime2lo Over a year ago

@TylerL I edited the response (sorry). It must be called with call not apply, using apply have to pass parameters as array. It should be makeGroup.call(duplicateEmployee, index2). Regards.

Tyler L Over a year ago

I think we're getting there. I'll modify the original question with your suggested update.

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