Awesome job on clearing the iterators lesson! You have learned a number of useful methods in this lesson as well as how to use the JavaScript documentation from the Mozilla Developer Network to discover and understand additional methods. Let’s review!

  • .forEach() is used to execute the same code on every element in an array but does not change the array and returns undefined.
  • .map() executes the same code on every element in an array and returns a new array with the updated elements.
  • .filter() checks every element in an array to see if it meets certain criteria and returns a new array with the elements that return truthy for the criteria.
  • .findIndex() returns the index of the first element of an array that satisfies a condition in the callback function. It returns -1 if none of the elements in the array satisfies the condition.
  • .reduce() iterates through an array and takes the values of the elements and returns a single value.
  • All iterator methods take a callback function, which can be a pre-defined function, a function expression, or an arrow function.
  • You can visit the Mozilla Developer Network to learn more about iterator methods (and all other parts of JavaScript!).


If you want to challenge yourself:

  • Define a callback function before you use it in a iterator.
  • Chain two iteration methods on the same array.
  • Use the optional arguments in an iterator to include the index or the entire array. (Check out MDN’s Array iteration methods page for more information)
  • Use .reduce() to take a multi-layered array and return a single layer array from scratch.

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