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JavaScript JavaScript Array Iteration Methods Combining Array Methods Chaining Array Methods

Posted by <noob />
<noob />
17,062 Points

Further explantion about the code in the teacher notes

Hi.

const numbers = [1, 1, 2, 3, 4, 3, 5, 5, 6, 7, 3, 8, 9, 10];

const unique = numbers.filter(function(number, index, array) {
  return index === array.indexOf(number);
});

console.log(unique); // => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

I'm a abit confused with this example so I'll be happy if someone can tell me if im right about this: I understand and tested the beahvir of "indexOf" which returns the first element that he encounter, in the first iteration "index" is 0 and the return statament return 0 === 0 and that's true so that number gets added to the unique numbers array.

in the second iteration, "index" is now 1 and the return statment evulate to 0, so we basically have 1===0 which is not true so the duplicate 1 is not added.

I added a console.log to see exactly whats happening in each iteration:

const numbers = [1, 1, 2, 3, 4, 3, 5, 5, 6, 7, 3, 8, 9, 10];

const unique = numbers.filter(function(number, index, array) {
  console.log(`the index is now ${index} and  result of the indexOf method is :${array.indexOf(number)}`);
  return index === array.indexOf(number)

});

console.log(unique); // => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

THE OUTPUT:

the index is now 0 and  result of the indexOf method is :0                       
the index is now 1 and  result of the indexOf method is :0                       
the index is now 2 and  result of the indexOf method is :2                       
the index is now 3 and  result of the indexOf method is :3                       
the index is now 4 and  result of the indexOf method is :4                       
the index is now 5 and  result of the indexOf method is :3                       
the index is now 6 and  result of the indexOf method is :6                       
the index is now 7 and  result of the indexOf method is :6                       
the index is now 8 and  result of the indexOf method is :8                       
the index is now 9 and  result of the indexOf method is :9                       
the index is now 10 and  result of the indexOf method is :3                      
the index is now 11 and  result of the indexOf method is :11                     
the index is now 12 and  result of the indexOf method is :12                     
the index is now 13 and  result of the indexOf method is :13

i hope this will help others to understand..