var numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var filtered = numbers.filter(function evenNumbers (number) {
return number % 2 === 0;
});
console.log(filtered);
I am total beginner to JavaScript, picking up the course offered by nodeschool. While in the exercise of "ARRAY FILTERING", I wonder what is the role of 'number' within the function evenNumbers as it was not declared beforehand.
It is declared, as a formal parameter to the callback evenNumbers (a function that takes an argument and tests whether it is even). filter will call the callback function once for each element of the array numbers, providing the element as the argument to the callback (which will assign it to number, via the usual function invocation process).
evenNumbers is the criterion for filter. You ask evenNumbers(1), it says false. evenNumbers(2), and it says true. filter will append each element to the result or not depening on what the callback function says; so 1 is not appended, and 2 is appended. Thus, the result ends up [2, 4, 6, 8, 10] with 1, 3, 5, 7 and 9 missing.numbers is an Array .filter is a method declared on Array.prototype.filter method accepts a callback function.,
Array.prototype.filter(callback[, thisArgs]) {
'''''
'''''
callback(currentElement, index, arrayObjectBeingTraversed)
});
So,
In your case,
callback --> function evenNumbers() {}
currentElement --> Number
