Uncaught TypeError: #<Object> is not a function

Question

The following function returns the index of an object:

selectedAppIndex: function () {
  console.log(this.activeApps)
  console.log(this.selectedApp)
  return this.activeApps.findIndex(this.selectedApp)
}

console.log(this.activeApps) logs the array:

console.log(this.selectedApp) logs the object:

As you can see the object in the array and the object in this.selectedApp is the same. So the function should output 0.

However I get this error:

Uncaught TypeError: #<Object> is not a function

(I'm using Chrome 49. And findIndex() is supported from Chrome 45.)

Answer 1

Your problem is due the fact that findIndex expect a function as a parameter not an object.

Inside of this function you define the condition to find the first the index of the first match.

For example if you are looking for the index of the number 12:

 function  search12(el){
      return el === 12;
 }

 [4, 6, 8, 12].findIndex(search12);

The above example will return the number 3, since 12 is located on the index 3.

Inside of the function that is passed to findIndex you have 3 parameters that can be used for test.

• element, is the current element being processed present in the original array.
• index, The index of the current element being processed, or the result if the test evaluates to true.
• array The original array findIndex was called upon.

More info.

As you can see on the function above you have to return the case where you have a match, because the function passed as a parameter is being executed every time per each element until is evaluated to true if some element evaluates to true will return that index if non element inside of the array evaluates to true will return -1

Answer 2

If you want to get the index of a value in an array, use indexOf:

return this.activeApps.indexOf(this.selectedApp)