Keling, JavaScript-da nima muhimligini, u bilan nimaga erisha olishimizni va qanday boshqa texnologiyalar bilan ushbu til yaxshi qo'llanilishini ko'rib chiqaylik.
JavaScript dastlab veb-sahifalarni jonlantirish uchun yaratilgan edi.
Ushbu tilda dasturlar skript deb nomlanadi. Ular veb-sahifani HTML-da yozilishi mumkin va sahifa brauzer tomonidan yuklanganidan keyin ular avtomatik ravishda amalga oshiriladi.
Skriptlar oddiy matn sifatida taqdim etiladi va amalga oshiriladi. Ularni ishga tushirish uchun maxsus tayyorgarlik yoki kompilatsiya kerak emas.
Shu jihatdan, JavaScript Java tilidan juda farq qiladi.
JavaScript yaratilganda, u dastlab "LiveScript" nomi bilan taqdim etilgan edi. Ammo Java o'sha paytlarda juda mashhur edi, shuning uchun Java tilining "ukasi" sifatida yangi tilni taqdim etish g'oyasi JS mashhur bo'lishga yordam beradi deb hisoblangan .
Ammo, rivojlanish jarayonida, JavaScript [ECMAScript](http://en.wikipedia.org/wiki/ECMAScript) deb ataladigan o'z xususiyatiga ega to'liq mustaqil tilga aylangan va hozirda Java tiliga hech qanday aloqasi yo'q.
Bugungi kunda JavaScript nafaqat brauzerda, balki serverda yoki aslida JavaScript interpretatori deb nomlangan maxsus dasturga ega bo'lgan har qanday qurilmada ham bajarilishi mumkin.
Brauzerlar o'z JavaScript interpretatorlariga ega, ular gohida "JavaScript virtual mashinasi" deb atalanadi.
Har bir intetptretatorni o'z nomi mavjud. Masalan:
<<<<<<< HEAD
- V8 -- Chrome va Opera brauzerlarida qo'llanadi.
- SpiderMonkey -- Firefox brauzerida.
- Explorer brauzerining turli xil versiyalari uchun "Trident" va "Chakra", Microsoft Edge uchun "ChakraCore", Safari uchun "Nitro" va "SquirrelFish" va boshqalar kabi boshqa kod nomlari mavjud.
Yuqoridagi atamalarni eslab qolish yaxshi, chunki ular netdagi ishlab chiquvchilar maqolalarida qo'llaniladi. Biz ulardan ham foydalanamiz. Masalan, agar "X funktsiyasini V8 qo'llab-quvvatlasa", ehtimol u Chrome va Opera-da ishlaydi.
- V8 -- in Chrome, Opera and Edge.
- SpiderMonkey -- in Firefox.
- ...There are other codenames like "Chakra" for IE, "JavaScriptCore", "Nitro" and "SquirrelFish" for Safari, etc.
The terms above are good to remember because they are used in developer articles on the internet. We'll use them too. For instance, if "a feature X is supported by V8", then it probably works in Chrome, Opera and Edge.
52c1e61915bc8970a950a3f59bd845827e49b4bf
Intetptretatorlar murakkab. Ammo asoslari oson.
<<<<<<< HEAD
1. Intetptretator (agar u brauzer bo'lsa, avtomatik o'rnatilgan) skriptni o'qiydi ("tahlil qiladi").
2. Keyin u skriptni mashina tiliga o'zgartiradi ("kompilyatsiya qiladi").
3. Va keyin mashina kodi juda tez ishlaydi.
=======
1. The engine (embedded if it's a browser) reads ("parses") the script.
2. Then it converts ("compiles") the script to machine code.
3. And then the machine code runs, pretty fast.
>>>>>>> 52c1e61915bc8970a950a3f59bd845827e49b4bf
Interpretatatsiya jarayonning har bir bosqichida optimallashtirishlarni qo'llaydi. U hattoki kompilyatsiya qilingan skriptni ishlayotganda kuzatib boradi, u orqali oqib o'tadigan ma'lumotlarni tahlil qiladi va shu bilimga asoslangan holda mashina kodiga optimallashtirishlarni qo'llaydi. Tugatgandan so'ng, skriptlar juda tez ishlaydi.
<<<<<<< HEAD Zamonaviy JavaScript - bu "xavfsiz" dasturlash tili. Bu xotira yoki protsessorga(CPU) past darajadagi kirishni ta'minlamaydi, chunki dastlab uni talab qilmaydigan brauzerlar uchun yaratilgan.
Modern JavaScript is a "safe" programming language. It does not provide low-level access to memory or the CPU, because it was initially created for browsers which do not require it.
52c1e61915bc8970a950a3f59bd845827e49b4bf
JavaScript-ning imkoniyatlari u ishlayotgan muhitga juda bog'liq. Masalan, Node.js JavaScript-ga o'zboshimchalik bilan fayllarni o'qish / yozish, tarmoq so'rovlarini bajarish va hk.
Brauzerda JavaScript veb-sahifani boshqarish, foydalanuvchi bilan o'zaro aloqasi va veb-server bilan bog'liq barcha narsani amalga oshirishi mumkin.
Masalan:
- Sahifaga yangi HTML qo'shish, mavjud tarkibni o'zgartirish, uslublarni o'zgartirish.
- Foydalanuvchining harakatlariga munosabat bildirish, sichqonchani bosish, ko'rsatgich harakatlari, tugmachalarni bosish bilan ishlash.
- Uzoq serverlarga tarmoq orqali so'rov yuboring, fayllarni yuklab olish va yuklash(deb nomlangan AJAX va COMET texnologiyalar).
- Cookies-ni olish va o'rnatish, tashrif buyuruvchiga savollar berish, xabarlarni ko'rsatish.
- Mijoz tomonidagi ma'lumotlarni eslab qolish("mahalliy saqlash").
<<<<<<< HEAD JavaScript-ning brauzerdagi imkoniyatlari foydalanuvchi xavfsizligi uchun cheklangan. Maqsad yomon veb-sahifaning shaxsiy ma'lumotlarga kirishini yoki foydalanuvchi ma'lumotlariga zarar etkazishini oldini olishdir.
JavaScript's abilities in the browser are limited to protect the user's safety. The aim is to prevent an evil webpage from accessing private information or harming the user's data.
52c1e61915bc8970a950a3f59bd845827e49b4bf
Bunday cheklovlarga quyidagilar kiradi:
-
Veb-sahifadagi JavaScript-ni qattiq diskdagi o'zboshimchalik bilan fayllarni o'qish / yozish, ularni nusxalash yoki dasturlarni bajarish mumkin emas. Uning OS tizimi funktsiyalariga to'g'ridan-to'g'ri kirish imkoniyati yo'q.
Zamonaviy brauzerlar unga fayllar bilan ishlashga imkon beradi, lekin kirish cheklangan va faqat foydalanuvchi brauzer oynasiga faylni "tushirish" yoki uni
<input>yorlig'i orqali tanlash kabi ba'zi bir amallarni bajargan taqdirdagina taqdim etiladi.
<<<<<<< HEAD Kamera/mikrofon va boshqa qurilmalar bilan o'zaro aloqa qilish usullari mavjud, ammo ular foydalanuvchidan aniq ruxsat talab qiladi. Shunday qilib, JavaScript-ni qo'llab-quvvatlaydigan sahifa veb-kamerani yashirincha yoqmasligi, atrofni kuzatishi va ma'lumotni NSA ga yuborishi mumkin emas.
-
Turli xil yorliqlar/oynalar odatda bir-birlarini bilishmaydi. Ba'zan ular bilishadi, masalan, bitta oyna ikkinchisini ochish uchun JavaScript-ni ishlatganda. Ammo bu holatda ham bitta sahifadagi JavaScript-ni boshqa saytlarga kirish mumkin emas, agar ular turli saytlardan (boshqa domendan, protokoldan yoki portdan) bo'lsa.
Bu "Xuddi shu manba siyosati"(Same origin policy) deyiladi. Buning uchun ikkala sahifa ma'lumotlar almashinuvi to'g'risida kelishib olishlari va uni boshqaradigan maxsus JavaScript kodini o'z ichiga olishi kerak. Biz buni o'quv qo'llanmasida ko'rib chiqamiz.
Ushbu cheklov, yana foydalanuvchi xavfsizligi uchun. Foydalanuvchi ochgan sahifa
http://anysite.comURL manzili bo'lgan boshqa brauzer yorlig'iga kira olmasligi kerakhttp://gmail.comva u erdan ma'lumotlarni o'g'irlash. -
JavaScript joriy sahifa kelgan serverga tarmoq orqali osongina aloqa qilish mumkin. Ammo uning boshqa saytlardan / domenlardan ma'lumotlarni qabul qilish qobiliyati nogiron. Iloji bo'lsa ham, bu uzoqdan aniq kelishuvni (HTTP sarlavhalarida ko'rsatilgan) talab qiladi. Yana bir bor bu xavfsizlikni cheklash.
Agar JavaScript brauzerdan tashqarida, masalan serverda ishlatilsa, bunday cheklovlar mavjud emas. Zamonaviy brauzerlar kengaytirilgan ruxsat so'rashi mumkin bo'lgan plagin / kengaytmalarga ham imkon beradi.
There are ways to interact with the camera/microphone and other devices, but they require a user's explicit permission. So a JavaScript-enabled page may not sneakily enable a web-camera, observe the surroundings and send the information to the [NSA](https://en.wikipedia.org/wiki/National_Security_Agency).
-
Different tabs/windows generally do not know about each other. Sometimes they do, for example when one window uses JavaScript to open the other one. But even in this case, JavaScript from one page may not access the other page if they come from different sites (from a different domain, protocol or port).
This is called the "Same Origin Policy". To work around that, both pages must agree for data exchange and must contain special JavaScript code that handles it. We'll cover that in the tutorial.
This limitation is, again, for the user's safety. A page from
http://anysite.comwhich a user has opened must not be able to access another browser tab with the URLhttp://gmail.com, for example, and steal information from there. -
JavaScript can easily communicate over the net to the server where the current page came from. But its ability to receive data from other sites/domains is severely limited. Though possible, it requires explicit agreement (expressed in HTTP headers) from the remote side. Once again, that's a safety limitation.
Such limitations do not exist if JavaScript is used outside of the browser, for example on a server. Modern browsers also allow plugins/extensions which may ask for extended permissions.
52c1e61915bc8970a950a3f59bd845827e49b4bf
JavaScript hech bo'lmaganda uchta ajoyib xususiyatga ega:
<<<<<<< HEAD
+ HTML va CSS bilan to'liq integratsiyasi.
+ Oson ishlar osongina amalga oshiriladi.
+ Barcha asosiy brauzerlar tomonidan qo'llab-quvvatlanadi va ularda standart sifatida yoqilgan.
=======
```compare
+ Full integration with HTML/CSS.
+ Simple things are done simply.
+ Supported by all major browsers and enabled by default.
>>>>>>> 52c1e61915bc8970a950a3f59bd845827e49b4bf
JavaScript - bu uchta narsani birlashtirgan yagona brauzer texnologiyasidir.
<<<<<<< HEAD Bu JavaScript-ni noyob qiladi. Shuning uchun u brauzer feyslarini yaratishda eng keng tarqalgan vositadir.
That said, JavaScript can be used to create servers, mobile applications, etc.
52c1e61915bc8970a950a3f59bd845827e49b4bf
Yangi texnologiyani o'rganishni rejalashtirayotib, uning istiqbollarini tekshirish ham muhimdir. Keling, zamonaviy tendentsiyalarga o'taylik.
JavaScript-ning sintaksisi hammaning ehtiyojlariga mos kelmaydi. Turli odamlar turli xususiyatlarni xohlashadi.
<<<<<<< HEAD Bu kutilgan hodisa bo'lishi kerak edi, chunki loyihalar va talablar har bir kishi uchun farq qiladi.
So, recently a plethora of new languages appeared, which are transpiled (converted) to JavaScript before they run in the browser.
52c1e61915bc8970a950a3f59bd845827e49b4bf
Shunday qilib, yaqinda juda ko'p yangi tillar paydo bo'ldi va brauzer ularni ishlatishdan oldin JavaScript-ga aylantirib bajaradi.
Zamonaviy asboblar transpilatsiyani juda tez va shaffof bajaradi, aslida dasturchilar kodni bitta tilda yozganda, ular uni avtomatik tarzda boshqa tilga aylantirish imkonini beradi.
<<<<<<< HEAD Bunday tillarning namunalari:
- CoffeeScript JavaScript uchun "sintaktik shakar" dir. Ushbu til bizga qisqa sintaksisni va aniqroq kodni taqdim etadi. Odatda, Ruby dasurchilari shu tilni afzal ko'rishadi.
- TypeScript murakkab tizimlarni ishlab chiqish, soddalashtirish va qo'llab-quvvatlash uchun "strict data typing"ni qo'shishga qaratilgan. Microsoft tomonidan ishlab chiqilgan.
- Dart brauzer bo'lmagan muhitda (mobil ilovalar kabi) ishlaydigan o'z dvigateliga ega bo'lgan mustaqil til. Bu dastlab JavaScript uchun zaxira sifatida Google tomonidan taklif etildi, lekin hozirgi paytda, brauzerlar shu tilni ham JS-ga transpilatsiya bo'lishini talab qilishadi. =======
- CoffeeScript is "syntactic sugar" for JavaScript. It introduces shorter syntax, allowing us to write clearer and more precise code. Usually, Ruby devs like it.
- TypeScript is concentrated on adding "strict data typing" to simplify the development and support of complex systems. It is developed by Microsoft.
- Flow also adds data typing, but in a different way. Developed by Facebook.
- Dart is a standalone language that has its own engine that runs in non-browser environments (like mobile apps), but also can be transpiled to JavaScript. Developed by Google.
- Brython is a Python transpiler to JavaScript that enables the writing of applications in pure Python without JavaScript.
- Kotlin is a modern, concise and safe programming language that can target the browser or Node.
There are more. Of course, even if we use one of these transpiled languages, we should also know JavaScript to really understand what we're doing.
52c1e61915bc8970a950a3f59bd845827e49b4bf
Bundan ham ko'proq tillar mavjud. Albatta, biz bu tillardan birini ishlatsak ham, biz nima qilayotganimizni tushunish uchun JavaScript-ni bilishimiz kerak.
<<<<<<< HEAD
- JavaScript dastlab brauzer tili sifatida yaratilgan, ammo hozirgi paytda ko'pgina boshqa muhitlarda ham qo'llanilmoqda.
- Bugun JavaScript HTML/CSS bilan to'la integratsiyalashgan va eng keng tarqalgan brauzer tili hisoblanadi.
- JavaScript-ga "aylanadigan" va muayyan xususiyatlarni taqdim etadigan ko'plab tillar mavjud. Javascriptni o'zlashtirgandan so'ng kamida qisqacha ularga bir nazar tashlash tavsiya etiladi. =======
- JavaScript was initially created as a browser-only language, but it is now used in many other environments as well.
- Today, JavaScript has a unique position as the most widely-adopted browser language, fully integrated with HTML/CSS.
- There are many languages that get "transpiled" to JavaScript and provide certain features. It is recommended to take a look at them, at least briefly, after mastering JavaScript.
52c1e61915bc8970a950a3f59bd845827e49b4bf