iterate without for loop javascript

Each time around the loop it just gives you the next item in the array. indentation is an (extremely rough) indicator of complexity, Let me know your thoughts via theTwitters, Subscribe to receive updates via the electronic mailsystem. Updated on August 26, 2021. In the previous article, we suggested that indentation is an (extremely rough) indicator of complexity. So, have we reduced complexity? JavaScript Without Loops - James Sinclair We call this pattern map. We have two functions that deal with strings: oodlify and izzlify. For example, the idea "Go five steps to the east" could be expressed this way as a loop: js To explore further, well expand our hero database to include some extra data: Now, lets say we have two problems. It looks something like this: This is a helpful construct because it puts all that counter boilerplate together at the top. on the 10thFebruary2017. Our goal is to write less complex JavaScript. We have separated the code for looping from the code that processes individual items. What we want is: Given an array and a function, map each item from the array into a new array. Loops and iteration - JavaScript | MDN - MDN Web Docs I would argue, yes. We use the predicate to decide whether or not to keep each item in heroes. You could accomplish the same thing with a while pretty easily as well. Is tabbing the best/only accessibility solution on a data heavy map UI? Reduced the problem from processing the whole array to just specifying what we want to do with each item. Atencio, Luis. Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned. But Ill leave you to try that out for yourself. But if we create an izzlifyArray() function were repeating ourselves again. Those functions dont have to know anything about arrays or looping. Lets consider an example. It is simple because we have separated concerns. So far, we havent looked at any concrete examples of how to do this. We dont have to read through all the generic loop code to work out that were filtering. @Mark I thought of that, but Array.forEach() always iterates over the entire array. For loops are declared with three optional expressions separated by semicolons: I just ran this snippet through JSLint. We go around the loop, keeping track of the strongest hero so far in strongest. How would I achieve that without using a for loop? So lets take a look at how loops in JavaScript work. We have another function, map that deals with arrays. Iterate with JavaScript For Loops You can run the same code multiple times by using a loop. I could filter inside the function but that seems really counter-intuitive. 2016, Functional Programming in JavaScript. Let the It just executes whatever function we pass it. But what if we wanted to add up an array of numbers? For example, we can write the same for statement without the initialization expression by initializing the variable outside of the loop. We dont have to worry about the details of how the iteration is happening. Filtering is very handy. It looks something like this: const len = input. We have a problem of the form Find all the heroes that. Note: I know I could disable the warning in JSLint, or that I could simply ignore the warning, but that just circumvents the issue. Iterate with JavaScript For Loops - freeCodeCamp.org But what if we wanted to find just one hero? And we have reduce to reduce an array down to a single value. What were trying to do is to run oodlify() on each item in the array and push the result into a new array. In addition, it implies code thats constantly changing or mutating in response to new iterations.. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. What is the libertarian solution to my setting's magical consequences for overpopulation? You can use any array method to loop through: for (array of populationArr){ console.log(array); } // Output: // ['male', 4] // ['female', 93] // ['others', 10] We could decide to destructure the array, so we get the key and value: for ([key, value] of populationArr){ console.log(key); } This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License. A definite improvement. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. In what ways was the Windows NT POSIX implementation unsuited to real use? If we use our hand-written reduce function, then the code is longer. The way weve written things here makes the code longer. The reduce function might seem fairly primitive at first glance. The Overflow #186: Do large language models know what theyre talking about? Note the lack of loops. But we definitely have a repeated pattern. If we want to do that we can write a recursive version: The recursive solution is quite elegant. What's the right way to say "bicycle wheel" in German? Its only useful if you want to create an array of exactly the same length as the input. This pattern is so common that JavaScript provides a simpler way of writing it: The for-loop. We dont even have to pull the item out of the array. Loop Through an Object in JavaScript - How to Iterate Over an Object in JS Well also rename the variables to further highlight similarities. We want to: Using a plain-old forof loop, we might write something like this: All things considered, this code isnt too bad. Using the built-in method, our code becomes: Now, if youre paying close attention, you may have noticed that this code is not much shorter. Also, there too many ways to iterate for any answer to be meaningful to such an open ended question. The forof loop does all that heavy lifting for us. Or find the shortest string in a list? This blew my mind a little bit when I first realised it. For this I'll continue to use the constructs that have served me well for decades. For Loops, ForOf Loops and ForIn Loops in JavaScript // Initialize a for statement with 5 iterations, // Manually increment variable by 1 four times, // Initalize for loop to run for the total length of an array, // Print names and values of object properties, // Iterate through each index in the string, [New] Build production-ready AI/ML applications with GPUs today! But it doesnt care what type of data is in the array, or even what you want to do with the data. All three expressions in the for loop are optional. Not the point. We would have removed a decent amount of complexity. Why is this code simple? receive updates. This pattern is so common that JavaScript provides a simpler way of writing it: The for-loop. That may seem like a stupid question, but think about it. That is. Realize instances but keeping the material. So, we create a function: This is starting to look much nicer, but what if we had another function we wanted to apply? But so far weve not seen any evidence of how that happens. Instead of mixing everything in together, weve separated string processing from array processing. And when we eliminate the loops we (almost always) reduce complexity and produce more maintainable code. Lets assume were using the built-in array methods for everything. How do I loop through or enumerate a JavaScript object? guide you to the right one. So we dont have to write our own version (unless we want to). Do this by applying the function to each item. The most common type of JavaScript loop is called a for loop because it runs for a specific number of times. Its free for anyone who subscribes to A map function for arrays looks like this: Of course, that still doesnt get rid of the loop entirely. Heres how I would refactor to iterate only once over the array: Its a little bit more complicated than the version where we iterate twice, but it may make a big difference if the array is enormous. We can make our code even more concise and expressive, but to see how, lets expand the problem a little. We can refactor it to reduce some of the repetition. What is the law on scanning pages from a copyright book for a friend? By using find our problem of finding a particular entry boils down to just one question: How do we know if weve found the thing we want? Learn more, Tutorial Series: How To Code in JavaScript, 1/37 How To Use the JavaScript Developer Console, 3/37 How To Write Your First JavaScript Program, 4/37 Understanding Syntax and Code Structure in JavaScript, 6/37 Understanding Data Types in JavaScript, 7/37 How To Work with Strings in JavaScript, 8/37 How To Index, Split, and Manipulate Strings in JavaScript, 9/37 How To Convert Data Types in JavaScript, 10/37 Understanding Variables, Scope, and Hoisting in JavaScript, 11/37 How To Do Math in JavaScript with Operators, 12/37 Understanding Comparison and Logical Operators in JavaScript, 14/37 How To Use Array Methods in JavaScript: Mutator Methods, 15/37 How To Use Array Methods in JavaScript: Accessor Methods, 16/37 How To Use Array Methods in JavaScript: Iteration Methods, 17/37 Understanding Objects in JavaScript, 18/37 Understanding Date and Time in JavaScript, 20/37 How To Work with JSON in JavaScript, 21/37 How To Write Conditional Statements in JavaScript, 22/37 How To Use the Switch Statement in JavaScript, 23/37 Using While Loops and DoWhile Loops in JavaScript, 24/37 For Loops, ForOf Loops and ForIn Loops in JavaScript, 25/37 How To Define Functions in JavaScript, 26/37 Understanding Prototypes and Inheritance in JavaScript, 27/37 Understanding Classes in JavaScript, 28/37 How To Use Object Methods in JavaScript, 29/37 Understanding This, Bind, Call, and Apply in JavaScript, 30/37 Understanding Map and Set Objects in JavaScript, 31/37 Understanding Generators in JavaScript, 32/37 Understanding Default Parameters in JavaScript, 33/37 Understanding Destructuring, Rest Parameters, and Spread Syntax in JavaScript, 34/37 Understanding Template Literals in JavaScript, 35/37 Understanding Arrow Functions in JavaScript, 36/37 Understanding the Event Loop, Callbacks, Promises, and Async/Await in JavaScript, 37/37 Understanding Modules and Import and Export Statements in JavaScript, How To Construct While and DoWhile Loops in JavaScript, Next in series: How To Define Functions in JavaScript ->. . A few people have pointed out that it feels inefficient to loop over the hero list twice in the reduce and filter examples. length; let output = []; for (let i = 0; i < len; i = i + 1) { let item = input[ i]; let newItem = oodlify( item); output.push( newItem); } Most examples with reduce do fairly simple things like adding numbers. In each case weve done three things: Notice that in each case, weve broken the problem down into solutions that use small, pure functions. We also have to keep comparing i to len so we know where to stop. But we can go further. You can create two counters that are updated simultaneously in a for loop using the comma operator. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Less complex. Written by James Sinclair So lets write a find function that will return the first item that matches: And again, JavaScript provides this one for us, so we dont have to write it ourselves: Once again, we end up expressing more information in less space. And as with our other iterators, using filter conveys more information in less space. Multiple let and var declarations can also be joined with commas. JavaScript for Loop - W3Schools But first, a little bit of setup. So, we have an array, and wed like to oodlify each entry. To make the loop pattern even clearer, well factor out the inner part of the loops into functions. How to iterate over part of an array without using a for loop How can I add new array elements at the beginning of an array in JavaScript? Ever forget which JavaScript array method does what? Civilised Guide to JavaScript Array Methods gently But having this approach of using a predicate function is neat. All we need to do is tell filter which items to keep. The obvious thing to do would be a loop for each: This works. @Airsick you asked, "What is JSLint's objection to this construction?". But we know that theres only one Black Widow and we can stop looking after weve found her. I find JSLint useful for some things, but I find its pedantry annoying at times, and although Douglas Crockford has some useful ideas, I have found them sometimes to be restrictive at best. Well create an example function and array to work with. It is also simple. The filter method looks at every single item in the array. We have map to do something with every item in an array. log (i);} It looks like this: This is much cleaner. And, just like map and reduce, JavaScript provides this one for us as an Array method. Lets do it anyway so we can see them side-by-side: Those two functions are scarily similar. iBooks. I'd considered the .slice() approach but thought there must be a more intuitive way of doing things. The only thing that really changes between the two is the function called and the initial value. But, its repetitivenot very DRY. Just two lines of code, and very little indentation. Either way, the order is still O(n). Thanks for your input. If we stopped here and used forof loops everywhere instead of for-loops, wed be doing well. With a while-loop, it looks something like this: Note that to keep track of where were up to, we use a counter, i. Whats really mind-blowing though, is that with just these four patterns (though there are others, and I encourage you to learn them), you can eliminate nearly all loops in your JS code. const arr = [1, 2, 3, 4, 5, 6]; for (let l = 0, r = arr.length - 1; l < r; l++, r--) { console.log(arr[l], arr[r]); } // 1 6 // 2 5 // 3 4. Say we have an array of hero objects: We would like to find the strongest hero. The end result is less complex code. Manning Publications. (Ep. Need Advice on Installing AC Unit in Antique Wooden Window Frame. Instead, its written right there in the method call. My questions is not about the specifics of the example, but why and how to achieve the same result without a 'for' loop. Our oodlifyArray() function wont help us now. How would this perform if the source array is large and the slice is of a similar order of magnitude? In fact, the only thing that really changes is our if-statement. This is because almost every loop we write in JS is processing an array, or building an array, or both. Is it simple because its short? We have to initialise the output array and call push() each time around the loop. You can think of a loop as a computerized version of the game where you tell someone to take X steps in one direction, then Y steps in another. But now that weve factored out our predicate functions, the repetition becomes clearer. We could use filter to find her, like so: The trouble with this is that its not very efficient. Why is using "forin" for array iteration a bad idea? Connect and share knowledge within a single location that is structured and easy to search. We can extract it out into a function. Using the built-in array methods, we only save about one line. The for statement creates a loop with 3 optional expressions: for ( expression 1; expression 2; expression 3) { // code block to be executed } Expression 1 is executed (one time) before the execution of the code block. In JavaScript we have at least four or five ways of looping. But generally, we dont tend to use the recursive version because it has bad performance characteristics in older browsers. a loop is an imperative control structure thats hard to reuse and difficult to plug in to other operations. This type of function that only returns true or false is sometimes called a predicate. Is it ethical to re-submit a manuscript without addressing comments from a particular reviewer while asking the editor to exclude them? What if we could abstract out the pattern here? That is why we can call this code simple. rev2023.7.14.43533. We forget about arrays and working variables. I can see that this would meet Douglas Crockford's desire to do away with loops, but I'd be concerned about performance. Find centralized, trusted content and collaborate around the technologies you use most. In this article we look at how to deal with JavaScript arrays, without using any loops. So, with ES2015, we now have a new loop construct that lets us forget about the counter: The forof loop. This code is now both concise and expressive. But how do you know which abstraction to use? Eliminated the loop control structure, so the code is more concise and (arguably) easier to read; Described the pattern were using by using the appropriate method name. Both reduce the array down to a single value. Please do not understand my answer as an endorsement of the JSlint rules, or an advise to use this code - it only shows a way to comply with the rules if you chose to follow them.

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