But, if you want to keep the original data intact, use. Whenever you need to change or interact with the original data in someway. I mentioned that .forEach() and .map() seem very similar. The same way a normal for loop would! However, in a cleaner more readable way! forEach() will now loop over your array and apply that function to each element. Whether that’s updating the element or changing it. In your function, you can grab the element passed and do something to it. forEach() takes a function, and that function requires you to provide one main argument…the element. This makes them both better for different things, which I’ll cover in a seconds. forEach() mutates (changes) the original array it’s call on, whereas .map() returns a new array. Yes, it does, except for one big difference… It works by taking a function and calling it on each item in an array. forEach() is a simpler and more readable way to write your standard for loop. If you have an array of products and need to total up the price, using .reduce just makes sense!īut you could also use it to find an average by dividing the total (accumulator) by the length of the array. Well, one thing you could do is total up an array of numbers. In addition to the function argument, you can also pass a second argument to represent the initial value at which your callback function should start totaling from. That value will now be stored as the accumulator. Your function should take the accumulator and element, perform an operation, and return a single value. The element represents the current element. The accumulator represents the accumulated total or result returned from the function you pass in. But only the element” and accumulator are required to make this puppy work. Those arguments are (accumulator, element, index, array). reduce() takes a function as an argument, and that function has access to the 4 arguments. But instead of return a new array, it takes a function in order to reduce the array to a single value. reduce(), like .map() and .filter() loops over an array. In case my explanation wasn’t quite up to scratch, I recommend checking out this post, written by a buddy of mine, Tom Rasmussen (aka over on Instagram). It enables me to take data from an array, pass it into a component, then return an array of components with the updated data. Personally, I find the method really useful when working with React. Or you could change all the text in an array to uppercase. If you have an array of objects, you could tell the function to extract the values of a particular property i.e. It all comes down to the function you define, but it has a ton of use cases. If you want, you could take that element and transform it in some way.įor example, concatenating something else onto each element, perform a calculation, or grab the property values from the elements and return that in a new array. Now you have access to the element in your function you can do cool stuff! But again, you only need element! So make sure you add a variable representing the element in the parameters of your function. Like.filter(), the function you pass has access to the same 3 arguments, element, index, array. map() on the end of an array, then pass a function into its parameters. It takes an array, loops through, and evokes a function on each element, then return the result in a new array.įirst, throw. map() works in a similar way to .filter(). Obviously, anywhere you need the ability to filter data, this method is a no-brainer! But it’s also great for adding some searching functionality to your projects. filter() does NOT change the original array, instead, it returns a NEW array. Make sure you return the result of your true or false test, because again, if you don’t. If the test returns true, the element is added to a new array, if not, it’s filtered out. Next, your function takes the element passed and performs a true or false test. filter to work you NEED to provide a variable name in the parameters of your function to represent the element. The only one you actually need is element.įor. The function you pass has access to 3 arguments provided by. This is the functions that will run a true or false test. filter() on your array and passing a function as an argument. filter() takes an array, loops through it and returns a new “filtered” array from all the elements that passed a true or false test specified in a function. JavaScript has some great built-in methods that can make your life 10 times easier! So let’s take a moment to explore my TOP 15 KILLER JavaScript methods. Let’s start this list with my favorite 3 array methods.
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