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GeezerVison is showing github.com — clean-code-javascript/README.md at master · theleancoder/clean-code-javascript Expand file tree/ Copy pathREADME.mdMore file actions 2183 lines (1806 loc) · 53.5 KB / Copy pathREADME.mdFile metadata and controls2183 lines (1806 loc) · 53.5 KB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 # clean-code-javascript ## Table of Contents 1. [Introduction](#introduction) 2. [Variables](#variables) 3. [Functions](#functions) 4. [Objects and Data Structures](#objects-and-data-structures) 5. [Classes](#classes) 6. [Testing](#testing) 7. [Concurrency](#concurrency) 8. [Error Handling](#error-handling) 9. [Formatting](#formatting) 10. [Comments](#comments) 11. [Translation](#translation) ## Introduction  Software engineering principles, from Robert C. Martin's book [*Clean Code*](https://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882), adapted for JavaScript. This is not a style guide. It's a guide to producing readable, reusable, and refactorable software in JavaScript. Not every principle herein has to be strictly followed, and even fewer will be universally agreed upon. These are guidelines and nothing more, but they are ones codified over many years of collective experience by the authors of *Clean Code*. Our craft of software engineering is just a bit over 50 years old, and we are still learning a lot. When software architecture is as old as architecture itself, maybe then we will have harder rules to follow. For now, let these guidelines serve as a touchstone by which to assess the quality of the JavaScript code that you and your team produce. One more thing: knowing these won't immediately make you a better software developer, and working with them for many years doesn't mean you won't make mistakes. Every piece of code starts as a first draft, like wet clay getting shaped into its final form. Finally, we chisel away the imperfections when we review it with our peers. Don't beat yourself up for first drafts that need improvement. Beat up the code instead! ## **Variables** ### Use meaningful and pronounceable variable names **Bad:** ```javascript const yyyymmdstr = moment().format('YYYY/MM/DD'); ``` **Good:** ```javascript const currentDate = moment().format('YYYY/MM/DD'); ``` **[⬆ back to top](#table-of-contents)** ### Use the same vocabulary for the same type of variable **Bad:** ```javascript getUserInfo(); getClientData(); getCustomerRecord(); ``` **Good:** ```javascript getUser(); ``` **[⬆ back to top](#table-of-contents)** ### Use searchable names We will read more code than we will ever write. It's important that the code we do write is readable and searchable. By *not* naming variables that end up being meaningful for understanding our program, we hurt our readers. Make your names searchable. Tools like [buddy.js](https://github.com/danielstjules/buddy.js) and [ESLint](https://github.com/eslint/eslint/blob/660e0918933e6e7fede26bc675a0763a6b357c94/docs/rules/no-magic-numbers.md) can help identify unnamed constants. **Bad:** ```javascript // What the heck is 86400000 for? setTimeout(blastOff, 86400000); ``` **Good:** ```javascript // Declare them as capitalized `const` globals. const MILLISECONDS_IN_A_DAY = 86400000; setTimeout(blastOff, MILLISECONDS_IN_A_DAY); ``` **[⬆ back to top](#table-of-contents)** ### Use explanatory variables **Bad:** ```javascript const address = 'One Infinite Loop, Cupertino 95014'; const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/; saveCityZipCode(address.match(cityZipCodeRegex)[1], address.match(cityZipCodeRegex)[2]); ``` **Good:** ```javascript const address = 'One Infinite Loop, Cupertino 95014'; const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/; const [, city, zipCode] = address.match(cityZipCodeRegex) || []; saveCityZipCode(city, zipCode); ``` **[⬆ back to top](#table-of-contents)** ### Avoid Mental Mapping Explicit is better than implicit. **Bad:** ```javascript const locations = ['Austin', 'New York', 'San Francisco']; locations.forEach((l) => { doStuff(); doSomeOtherStuff(); // ... // ... // ... // Wait, what is `l` for again? dispatch(l); }); ``` **Good:** ```javascript const locations = ['Austin', 'New York', 'San Francisco']; locations.forEach((location) => { doStuff(); doSomeOtherStuff(); // ... // ... // ... dispatch(location); }); ``` **[⬆ back to top](#table-of-contents)** ### Don't add unneeded context If your class/object name tells you something, don't repeat that in your variable name. **Bad:** ```javascript const Car = { carMake: 'Honda', carModel: 'Accord', carColor: 'Blue' }; function paintCar(car) { car.carColor = 'Red'; } ``` **Good:** ```javascript const Car = { make: 'Honda', model: 'Accord', color: 'Blue' }; function paintCar(car) { car.color = 'Red'; } ``` **[⬆ back to top](#table-of-contents)** ### Use default arguments instead of short circuiting or conditionals **Bad:** ```javascript function createMicrobrewery(name) { const breweryName = name || 'Hipster Brew Co.'; // ... } ``` **Good:** ```javascript function createMicrobrewery(breweryName = 'Hipster Brew Co.') { // ... } ``` **[⬆ back to top](#table-of-contents)** ## **Functions** ### Function arguments (2 or fewer ideally) Limiting the amount of function parameters is incredibly important because it makes testing your function easier. Having more than three leads to a combinatorial explosion where you have to test tons of different cases with each separate argument. One or two arguments is the ideal case, and three should be avoided if possible. Anything more than that should be consolidated. Usually, if you have more than two arguments then your function is trying to do too much. In cases where it's not, most of the time a higher-level object will suffice as an argument. Since JavaScript allows you to make objects on the fly, without a lot of class boilerplate, you can use an object if you are finding yourself needing a lot of arguments. To make it obvious what properties the function expects, you can use the es6 destructuring syntax. This has a few advantages: 1. When someone looks at the function signature, it's immediately clear what properties are being used. 2. Destructuring also clones the specified primitive values of the argument object passed into the function. This can help prevent side effects. Note: objects and arrays that are destructured from the argument object are NOT cloned. 3. Linters can warn you about unused properties, which would be impossible without destructuring. **Bad:** ```javascript function createMenu(title, body, buttonText, cancellable) { // ... } ``` **Good:** ```javascript function createMenu({ title, body, buttonText, cancellable }) { // ... } createMenu({ title: 'Foo', body: 'Bar', buttonText: 'Baz', cancellable: true }); ``` **[⬆ back to top](#table-of-contents)** ### Functions should do one thing This is by far the most important rule in software engineering. When functions do more than one thing, they are harder to compose, test, and reason about. When you can isolate a function to just one action, they can be refactored easily and your code will read much cleaner. If you take nothing else away from this guide other than this, you'll be ahead of many developers. **Bad:** ```javascript function emailClients(clients) { clients.forEach((client) => { const clientRecord = database.lookup(client); if (clientRecord.isActive()) { email(client); } }); } ``` **Good:** ```javascript function emailClients(clients) { clients .filter(isClientActive) .forEach(email); } function isClientActive(client) { const clientRecord = database.lookup(client); return clientRecord.isActive(); } ``` **[⬆ back to top](#table-of-contents)** ### Function names should say what they do **Bad:** ```javascript function addToDate(date, month) { // ... } const date = new Date(); // It's hard to to tell from the function name what is added addToDate(date, 1); ``` **Good:** ```javascript function addMonthToDate(month, date) { // ... } const date = new Date(); addMonthToDate(1, date); ``` **[⬆ back to top](#table-of-contents)** ### Functions should only be one level of abstraction When you have more than one level of abstraction your function is usually doing too much. Splitting up functions leads to reusability and easier testing. **Bad:** ```javascript function parseBetterJSAlternative(code) { const REGEXES = [ // ... ]; const statements = code.split(' '); const tokens = []; REGEXES.forEach((REGEX) => { statements.forEach((statement) => { // ... }); }); const ast = []; tokens.forEach((token) => { // lex... }); ast.forEach((node) => { // parse... }); } ``` **Good:** ```javascript function tokenize(code) { const REGEXES = [ // ... ]; const statements = code.split(' '); const tokens = []; REGEXES.forEach((REGEX) => { statements.forEach((statement) => { tokens.push( /* ... */ ); }); }); return tokens; } function lexer(tokens) { const ast = []; tokens.forEach((token) => { ast.push( /* ... */ ); }); return ast; } function parseBetterJSAlternative(code) { const tokens = tokenize(code); const ast = lexer(tokens); ast.forEach((node) => { // parse... }); } ``` **[⬆ back to top](#table-of-contents)** ### Remove duplicate code Do your absolute best to avoid duplicate code. Duplicate code is bad because it means that there's more than one place to alter something if you need to change some logic. Imagine if you run a restaurant and you keep track of your inventory: all your tomatoes, onions, garlic, spices, etc. If you have multiple lists that you keep this on, then all have to be updated when you serve a dish with tomatoes in them. If you only have one list, there's only one place to update! Oftentimes you have duplicate code because you have two or more slightly different things, that share a lot in common, but their differences force you to have two or more separate functions that do much of the same things. Removing duplicate code means creating an abstraction that can handle this set of different things with just one function/module/class. Getting the abstraction right is critical, that's why you should follow the SOLID principles laid out in the *Classes* section. Bad abstractions can be worse than duplicate code, so be careful! Having said this, if you can make a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself updating multiple places anytime you want to change one thing. **Bad:** ```javascript function showDeveloperList(developers) { developers.forEach((developer) => { const expectedSalary = developer.calculateExpectedSalary(); const experience = developer.getExperience(); const githubLink = developer.getGithubLink(); const data = { expectedSalary, experience, githubLink }; render(data); }); } function showManagerList(managers) { managers.forEach((manager) => { const expectedSalary = manager.calculateExpectedSalary(); const experience = manager.getExperience(); const portfolio = manager.getMBAProjects(); const data = { expectedSalary, experience, portfolio }; render(data); }); } ``` **Good:** ```javascript function showList(employees) { employees.forEach((employee) => { const expectedSalary = employee.calculateExpectedSalary(); const experience = employee.getExperience(); let portfolio = employee.getGithubLink(); if (employee.type === 'manager') { portfolio = employee.getMBAProjects(); } const data = { expectedSalary, experience, portfolio }; render(data); }); } ``` **[⬆ back to top](#table-of-contents)** ### Set default objects with Object.assign **Bad:** ```javascript const menuConfig = { title: null, body: 'Bar', buttonText: null, cancellable: true }; function createMenu(config) { config.title = config.title || 'Foo'; config.body = config.body || 'Bar'; config.buttonText = config.buttonText || 'Baz'; config.cancellable = config.cancellable === undefined ? config.cancellable : true; } createMenu(menuConfig); ``` **Good:** ```javascript const menuConfig = { title: 'Order', // User did not include 'body' key buttonText: 'Send', cancellable: true }; function createMenu(config) { config = Object.assign({ title: 'Foo', body: 'Bar', buttonText: 'Baz', cancellable: true }, config); // config now equals: {title: "Order", body: "Bar", buttonText: "Send", cancellable: true} // ... } createMenu(menuConfig); ``` **[⬆ back to top](#table-of-contents)** ### Don't use flags as function parameters Flags tell your user that this function does more than one thing. Functions should do one thing. Split out your functions if they are following different code paths based on a boolean. **Bad:** ```javascript function createFile(name, temp) { if (temp) { fs.create(`./temp/${name}`); } else { fs.create(name); } } ``` **Good:** ```javascript function createFile(name) { fs.create(name); } function createTempFile(name) { createFile(`./temp/${name}`); } ``` **[⬆ back to top](#table-of-contents)** ### Avoid Side Effects (part 1) A function produces a side effect if it does anything other than take a value in and return another value or values. A side effect could be writing to a file, modifying some global variable, or accidentally wiring all your money to a stranger. Now, you do need to have side effects in a program on occasion. Like the previous example, you might need to write to a file. What you want to do is to centralize where you are doing this. Don't have several functions and classes that write to a particular file. Have one service that does it. One and only one. The main point is to avoid common pitfalls like sharing state between objects without any structure, using mutable data types that can be written to by anything, and not centralizing where your side effects occur. If you can do this, you will be happier than the vast majority of other programmers. **Bad:** ```javascript // Global variable referenced by following function. // If we had another function that used this name, now it'd be an array and it could break it. let name = 'Ryan McDermott'; function splitIntoFirstAndLastName() { name = name.split(' '); } splitIntoFirstAndLastName(); console.log(name); // ['Ryan', 'McDermott']; ``` **Good:** ```javascript function splitIntoFirstAndLastName(name) { return name.split(' '); } const name = 'Ryan McDermott'; const newName = splitIntoFirstAndLastName(name); console.log(name); // 'Ryan McDermott'; console.log(newName); // ['Ryan', 'McDermott']; ``` **[⬆ back to top](#table-of-contents)** ### Avoid Side Effects (part 2) In JavaScript, primitives are passed by value and objects/arrays are passed by reference. In the case of objects and arrays, if our function makes a change in a shopping cart array, for example, by adding an item to purchase, then any other function that uses that `cart` array will be affected by this addition. That may be great, however it can be bad too. Let's imagine a bad situation: The user clicks the "Purchase", button which calls a `purchase` function that spawns a network request and sends the `cart` array to the server. Because of a bad network connection, the `purchase` function has to keep retrying the request. Now, what if in the meantime the user accidentally clicks "Add to Cart" button on an item they don't actually want before the network request begins? If that happens and the network request begins, then that purchase function will send the accidentally added item because it has a reference to a shopping cart array that the `addItemToCart` function modified by adding an unwanted item. A great solution would be for the `addItemToCart` to always clone the `cart`, edit it, and return the clone. This ensures that no other functions that are holding onto a reference of the shopping cart will be affected by any changes. Two caveats to mention to this approach: 1. There might be cases where you actually want to modify the input object, but when you adopt this programming practice you will find that those case are pretty rare. Most things can be refactored to have no side effects! 2. Cloning big objects can be very expensive in terms of performance. Luckily, this isn't a big issue in practice because there are [great libraries](https://facebook.github.io/immutable-js/) that allow this kind of programming approach to be fast and not as memory intensive as it would be for you to manually clone objects and arrays. **Bad:** ```javascript const addItemToCart = (cart, item) => { cart.push({ item, date: Date.now() }); }; ``` **Good:** ```javascript const addItemToCart = (cart, item) => { return [...cart, { item, date : Date.now() }]; }; ``` **[⬆ back to top](#table-of-contents)** ### Don't write to global functions Polluting globals is a bad practice in JavaScript because you could clash with another library and the user of your API would be none-the-wiser until they get an exception in production. Let's think about an example: what if you wanted to extend JavaScript's native Array method to have a `diff` method that could show the difference between two arrays? You could write your new function to the `Array.prototype`, but it could clash with another library that tried to do the same thing. What if that other library was just using `diff` to find the difference between the first and last elements of an array? This is why it would be much better to just use ES2015/ES6 classes and simply extend the `Array` global. **Bad:** ```javascript Array.prototype.diff = function diff(comparisonArray) { const hash = new Set(comparisonArray); return this.filter(elem => !hash.has(elem)); }; ``` **Good:** ```javascript class SuperArray extends Array { diff(comparisonArray) { const hash = new Set(comparisonArray); return this.filter(elem => !hash.has(elem)); } } ``` **[⬆ back to top](#table-of-contents)** ### Favor functional programming over imperative programming JavaScript isn't a functional language in the way that Haskell is, but it has a functional flavor to it. Functional languages are cleaner and easier to test. Favor this style of programming when you can. **Bad:** ```javascript const programmerOutput = [ { name: 'Uncle Bobby', linesOfCode: 500 }, { name: 'Suzie Q', linesOfCode: 1500 }, { name: 'Jimmy Gosling', linesOfCode: 150 }, { name: 'Gracie Hopper', linesOfCode: 1000 } ]; let totalOutput = 0; for (let i = 0; i < programmerOutput.length; i++) { totalOutput += programmerOutput[i].linesOfCode; } ``` **Good:** ```javascript const programmerOutput = [ { name: 'Uncle Bobby', linesOfCode: 500 }, { name: 'Suzie Q', linesOfCode: 1500 }, { name: 'Jimmy Gosling', linesOfCode: 150 }, { name: 'Gracie Hopper', linesOfCode: 1000 } ]; const INITIAL_VALUE = 0; const totalOutput = programmerOutput .map((programmer) => programmer.linesOfCode) .reduce((acc, linesOfCode) => acc + linesOfCode, INITIAL_VALUE); ``` **[⬆ back to top](#table-of-contents)** ### Encapsulate conditionals **Bad:** ```javascript if (fsm.state === 'fetching' && isEmpty(listNode)) { // ... } ``` **Good:** ```javascript function shouldShowSpinner(fsm, listNode) { return fsm.state === 'fetching' && isEmpty(listNode); } if (shouldShowSpinner(fsmInstance, listNodeInstance)) { // ... } ``` **[⬆ back to top](#table-of-contents)** ### Avoid negative conditionals **Bad:** ```javascript function isDOMNodeNotPresent(node) { // ... } if (!isDOMNodeNotPresent(node)) { // ... } ``` **Good:** ```javascript function isDOMNodePresent(node) { // ... } if (isDOMNodePresent(node)) { // ... } ``` **[⬆ back to top](#table-of-contents)** ### Avoid conditionals This seems like an impossible task. Upon first hearing this, most people say, "how am I supposed to do anything without an `if` statement?" The answer is that you can use polymorphism to achieve the same task in many cases. The second question is usually, "well that's great but why would I want to do that?" The answer is a previous clean code concept we learned: a function should only do one thing. When you have classes and functions that have `if` statements, you are telling your user that your function does more than one thing. Remember, just do one thing. **Bad:** ```javascript class Airplane { // ... getCruisingAltitude() { switch (this.type) { case '777': return this.getMaxAltitude() - this.getPassengerCount(); case 'Air Force One': return this.getMaxAltitude(); case 'Cessna': return this.getMaxAltitude() - this.getFuelExpenditure(); } } } ``` **Good:** ```javascript class Airplane { // ... } class Boeing777 extends Airplane { // ... getCruisingAltitude() { return this.getMaxAltitude() - this.getPassengerCount(); } } class AirForceOne extends Airplane { // ... getCruisingAltitude() { return this.getMaxAltitude(); } } class Cessna extends Airplane { // ... getCruisingAltitude() { return this.getMaxAltitude() - this.getFuelExpenditure(); } } ``` **[⬆ back to top](#table-of-contents)** ### Avoid type-checking (part 1) JavaScript is untyped, which means your functions can take any type of argument. Sometimes you are bitten by this freedom and it becomes tempting to do type-checking in your functions. There are many ways to avoid having to do this. The first thing to consider is consistent APIs. **Bad:** ```javascript function travelToTexas(vehicle) { if (vehicle instanceof Bicycle) { vehicle.pedal(this.currentLocation, new Location('texas')); } else if (vehicle instanceof Car) { vehicle.drive(this.currentLocation, new Location('texas')); } } ``` **Good:** ```javascript function travelToTexas(vehicle) { vehicle.move(this.currentLocation, new Location('texas')); } ``` **[⬆ back to top](#table-of-contents)** ### Avoid type-checking (part 2) If you are working with basic primitive values like strings, integers, and arrays, and you can't use polymorphism but you still feel the need to type-check, you should consider using TypeScript. It is an excellent alternative to normal JavaScript, as it provides you with static typing on top of standard JavaScript syntax. The problem with manually type-checking normal JavaScript is that doing it well requires so much extra verbiage that the faux "type-safety" you get doesn't make up for the lost readability. Keep your JavaScript clean, write good tests, and have good code reviews. Otherwise, do all of that but with TypeScript (which, like I said, is a great alternative!). **Bad:** ```javascript function combine(val1, val2) { if (typeof val1 === 'number' && typeof val2 === 'number' || typeof val1 === 'string' && typeof val2 === 'string') { return val1 + val2; } throw new Error('Must be of type String or Number'); } ``` **Good:** ```javascript function combine(val1, val2) { return val1 + val2; } ``` **[⬆ back to top](#table-of-contents)** ### Don't over-optimize Modern browsers do a lot of optimization under-the-hood at runtime. A lot of times, if you are optimizing then you are just wasting your time. [There are good resources](https://github.com/petkaantonov/bluebird/wiki/Optimization-killers) for seeing where optimization is lacking. Target those in the meantime, until they are fixed if they can be. **Bad:** ```javascript // On old browsers, each iteration with uncached `list.length` would be costly // because of `list.length` recomputation. In modern browsers, this is optimized. for (let i = 0, len = list.length; i < len; i++) { // ... } ``` **Good:** ```javascript for (let i = 0; i < list.length; i++) { // ... } ``` **[⬆ back to top](#table-of-contents)** ### Remove dead code Dead code is just as bad as duplicate code. There's no reason to keep it in your codebase. If it's not being called, get rid of it! It will still be safe in your version history if you still need it. **Bad:** ```javascript function oldRequestModule(url) { // ... } function newRequestModule(url) { // ... } const req = newRequestModule; inventoryTracker('apples', req, 'www.inventory-awesome.io'); ``` **Good:** ```javascript function newRequestModule(url) { // ... } const req = newRequestModule; inventoryTracker('apples', req, 'www.inventory-awesome.io'); ``` **[⬆ back to top](#table-of-contents)** ## **Objects and Data Structures** ### Use getters and setters JavaScript doesn't have interfaces or types so it is very hard to enforce this pattern, because we don't have keywords like `public` and `private`. As it is, using getters and setters to access data on objects is far better than simply looking for a property on an object. "Why?" you might ask. Well, here's an unorganized list of reasons why: * When you want to do more beyond getting an object property, you don't have to look up and change every accessor in your codebase. * Makes adding validation simple when doing a `set`. * Encapsulates the internal representation. * Easy to add logging and error handling when getting and setting. * Inheriting this class, you can override default functionality. * You can lazy load your object's properties, let's say getting it from a server. **Bad:** ```javascript class BankAccount { constructor() { this.balance = 1000; } } const bankAccount = new BankAccount(); // Buy shoes... bankAccount.balance -= 100; ``` **Good:** ```javascript class BankAccount { constructor(balance = 1000) { this._balance = balance; } // It doesn't have to be prefixed with `get` or `set` to be a getter/setter set balance(amount) { if (this.verifyIfAmountCanBeSetted(amount)) { this._balance = amount; } } get balance() { return this._balance; } verifyIfAmountCanBeSetted(val) { // ... } } const bankAccount = new BankAccount(); // Buy shoes... bankAccount.balance -= shoesPrice; // Get balance let balance = bankAccount.balance; ``` **[⬆ back to top](#table-of-contents)** ### Make objects have private members This can be accomplished through closures (for ES5 and below). **Bad:** ```javascript const Employee = function(name) { this.name = name; }; |
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