JavaScript 字面量77788

JavaScript 语法

JavaScript 是一个程序语言。语法规则定义了语言结构。

JavaScript 语法

JavaScript 是一个脚本语言。

它是一个轻量级，但功能强大的编程语言。

JavaScript 字面量

在编程语言中，一般固定值称为字面量，如 3.14。

数字（Number）字面量 可以是整数或者是小数，或者是科学计数(e)。

3.14 1001 https://avg.163.com/topic/detail/12449497 https://avg.163.com/topic/detail/12449496 https://avg.163.com/topic/detail/12449495 https://avg.163.com/topic/detail/12449492 https://avg.163.com/topic/detail/12449491 https://avg.163.com/topic/detail/12449490 https://avg.163.com/topic/detail/12449489 https://avg.163.com/topic/detail/12449488 https://avg.163.com/topic/detail/12449487 https://avg.163.com/topic/detail/12449486 https://avg.163.com/topic/detail/12449485 https://avg.163.com/topic/detail/12449484 https://avg.163.com/topic/detail/12449480 https://avg.163.com/topic/detail/12449481 https://avg.163.com/topic/detail/12449449 https://avg.163.com/topic/detail/12449478 https://avg.163.com/topic/detail/12449479 https://avg.163.com/topic/detail/12449463 https://avg.163.com/topic/detail/12449447 https://avg.163.com/topic/detail/12449466 https://avg.163.com/topic/detail/12449477 https://avg.163.com/topic/detail/12449475 https://avg.163.com/topic/detail/12449471 https://avg.163.com/topic/detail/12449473 https://avg.163.com/topic/detail/12449476 https://avg.163.com/topic/detail/12449474 https://avg.163.com/topic/detail/12449468 https://avg.163.com/topic/detail/12449469 https://avg.163.com/topic/detail/12449458 https://avg.163.com/topic/detail/12449247 https://avg.163.com/topic/detail/12449461 https://avg.163.com/topic/detail/12449464 https://avg.163.com/topic/detail/12449460 https://avg.163.com/topic/detail/12449455 https://avg.163.com/topic/detail/12449453 https://avg.163.com/topic/detail/12449456 https://avg.163.com/topic/detail/12449451 https://avg.163.com/topic/detail/12449277 https://avg.163.com/topic/detail/12449219 https://avg.163.com/topic/detail/12449249 https://avg.163.com/topic/detail/12449256 https://avg.163.com/topic/detail/12449232 https://avg.163.com/topic/detail/12449457 https://avg.163.com/topic/detail/12449454 https://avg.163.com/topic/detail/12449450 https://avg.163.com/topic/detail/12449452 https://avg.163.com/topic/detail/12449448 https://avg.163.com/topic/detail/12449446 https://avg.163.com/topic/detail/12449445 https://avg.163.com/topic/detail/12449444 https://avg.163.com/topic/detail/12449442 https://avg.163.com/topic/detail/12449443 https://avg.163.com/topic/detail/12449440 https://avg.163.com/topic/detail/12449441 https://avg.163.com/topic/detail/12449439 https://avg.163.com/topic/detail/12449437 https://avg.163.com/topic/detail/12449436 https://avg.163.com/topic/detail/12449435 https://avg.163.com/topic/detail/12449434 https://avg.163.com/topic/detail/12449433 https://avg.163.com/topic/detail/12449432 https://avg.163.com/topic/detail/12449431 https://avg.163.com/topic/detail/12449430 https://avg.163.com/topic/detail/12449428 https://avg.163.com/topic/detail/12449429 https://avg.163.com/topic/detail/12449427 https://avg.163.com/topic/detail/12449426 https://avg.163.com/topic/detail/12449425 https://avg.163.com/topic/detail/12449424 https://avg.163.com/topic/detail/12449423 https://avg.163.com/topic/detail/12449422 https://avg.163.com/topic/detail/12449421 https://avg.163.com/topic/detail/12449420 https://avg.163.com/topic/detail/12449418 https://avg.163.com/topic/detail/12449419 https://avg.163.com/topic/detail/12449416 https://avg.163.com/topic/detail/12449414 https://avg.163.com/topic/detail/12449417 https://avg.163.com/topic/detail/12449415 https://avg.163.com/topic/detail/12449413 https://avg.163.com/topic/detail/12449412 https://avg.163.com/topic/detail/12449409 https://avg.163.com/topic/detail/12449410 https://avg.163.com/topic/detail/12449408 https://avg.163.com/topic/detail/12449407 https://avg.163.com/topic/detail/12449406 https://avg.163.com/topic/detail/12449405 https://avg.163.com/topic/detail/12449404 https://avg.163.com/topic/detail/12449403 https://avg.163.com/topic/detail/12449402 https://avg.163.com/topic/detail/12449401 https://avg.163.com/topic/detail/12449399 https://avg.163.com/topic/detail/12449398 https://avg.163.com/topic/detail/12449396 https://avg.163.com/topic/detail/12449400 https://avg.163.com/topic/detail/12448489 https://avg.163.com/topic/detail/12448264 https://avg.163.com/topic/detail/12449391 https://avg.163.com/topic/detail/12448490 https://avg.163.com/topic/detail/12449393 https://avg.163.com/topic/detail/12449392 https://avg.163.com/topic/detail/12449390 https://avg.163.com/topic/detail/12449388 https://avg.163.com/topic/detail/12449389 https://avg.163.com/topic/detail/12449387 https://avg.163.com/topic/detail/12449382 https://avg.163.com/topic/detail/12449386 https://avg.163.com/topic/detail/12449384 https://avg.163.com/topic/detail/12449383 https://avg.163.com/topic/detail/12449379 https://avg.163.com/topic/detail/12449376 https://avg.163.com/topic/detail/12449381 https://avg.163.com/topic/detail/12449380 https://avg.163.com/topic/detail/12449378 https://avg.163.com/topic/detail/12449375 https://avg.163.com/topic/detail/12449377 https://avg.163.com/topic/detail/12449374 https://avg.163.com/topic/detail/12449373 https://avg.163.com/topic/detail/12449372 https://avg.163.com/topic/detail/12449371 https://avg.163.com/topic/detail/12449370 https://avg.163.com/topic/detail/12449362 https://avg.163.com/topic/detail/12449367 https://avg.163.com/topic/detail/12449369 https://avg.163.com/topic/detail/12449366 https://avg.163.com/topic/detail/12449368 https://avg.163.com/topic/detail/12449364 https://avg.163.com/topic/detail/12449363 https://avg.163.com/topic/detail/12449360 https://avg.163.com/topic/detail/12449361 https://avg.163.com/topic/detail/12449359 https://avg.163.com/topic/detail/12449358 https://avg.163.com/topic/detail/12449357 https://avg.163.com/topic/detail/12449356 https://avg.163.com/topic/detail/12449355 https://avg.163.com/topic/detail/12449354 https://avg.163.com/topic/detail/12449353 https://avg.163.com/topic/detail/12449352 https://avg.163.com/topic/detail/12449351 https://avg.163.com/topic/detail/12449344 https://avg.163.com/topic/detail/12449345 https://avg.163.com/topic/detail/12449350 https://avg.163.com/topic/detail/12449349 https://avg.163.com/topic/detail/12449347 https://avg.163.com/topic/detail/12449346 https://avg.163.com/topic/detail/12449343 https://avg.163.com/topic/detail/12449342 https://avg.163.com/topic/detail/12449341 https://avg.163.com/topic/detail/12449339 https://avg.163.com/topic/detail/12449337 https://avg.163.com/topic/detail/12449336 https://avg.163.com/topic/detail/12449338 https://avg.163.com/topic/detail/12449335 https://avg.163.com/topic/detail/12449334 https://avg.163.com/topic/detail/12449333 https://avg.163.com/topic/detail/12449330 https://avg.163.com/topic/detail/12449329 https://avg.163.com/topic/detail/12449332 https://avg.163.com/topic/detail/12449331 https://avg.163.com/topic/detail/12449327 https://avg.163.com/topic/detail/12448404 https://avg.163.com/topic/detail/12448472 https://avg.163.com/topic/detail/12448449 https://avg.163.com/topic/detail/12449321 https://avg.163.com/topic/detail/12448435 https://avg.163.com/topic/detail/12448432 https://avg.163.com/topic/detail/12449317 https://avg.163.com/topic/detail/12449319 https://avg.163.com/topic/detail/12449318 https://avg.163.com/topic/detail/12449316 https://avg.163.com/topic/detail/12449315 https://avg.163.com/topic/detail/12449313 https://avg.163.com/topic/detail/12449312 https://avg.163.com/topic/detail/12449310 https://avg.163.com/topic/detail/12449311 https://avg.163.com/topic/detail/12449309 https://avg.163.com/topic/detail/12449308 https://avg.163.com/topic/detail/12449307 https://avg.163.com/topic/detail/12449306 https://avg.163.com/topic/detail/12449305 https://avg.163.com/topic/detail/12449304 https://avg.163.com/topic/detail/12449302 https://avg.163.com/topic/detail/12449301 https://avg.163.com/topic/detail/12449298 https://avg.163.com/topic/detail/12449295 https://avg.163.com/topic/detail/12449294 https://avg.163.com/topic/detail/12449290 https://avg.163.com/topic/detail/12449291 https://avg.163.com/topic/detail/12449289 https://avg.163.com/topic/detail/12449288 https://avg.163.com/topic/detail/12449287 https://avg.163.com/topic/detail/12449282 https://avg.163.com/topic/detail/12449285 https://avg.163.com/topic/detail/12449284 https://avg.163.com/topic/detail/12449283 https://avg.163.com/topic/detail/12449274 https://avg.163.com/topic/detail/12449279 https://avg.163.com/topic/detail/12449281 https://avg.163.com/topic/detail/12449280 https://avg.163.com/topic/detail/12449273 https://avg.163.com/topic/detail/12449271 https://avg.163.com/topic/detail/12449270 https://avg.163.com/topic/detail/12448385 https://avg.163.com/topic/detail/12449268 https://avg.163.com/topic/detail/12448434 https://avg.163.com/topic/detail/12448400 https://avg.163.com/topic/detail/12448395 https://avg.163.com/topic/detail/12448379 https://avg.163.com/topic/detail/12449267 https://avg.163.com/topic/detail/12448376 https://avg.163.com/topic/detail/12449265 https://avg.163.com/topic/detail/12449264 https://avg.163.com/topic/detail/12449263 https://avg.163.com/topic/detail/12449262 https://avg.163.com/topic/detail/12449259 https://avg.163.com/topic/detail/12449260 https://avg.163.com/topic/detail/12449256 https://avg.163.com/topic/detail/12449258 https://avg.163.com/topic/detail/12449257 https://avg.163.com/topic/detail/12449255 https://avg.163.com/topic/detail/12449254 https://avg.163.com/topic/detail/12449252 https://avg.163.com/topic/detail/12449253 https://avg.163.com/topic/detail/12449251 https://avg.163.com/topic/detail/12449250 https://avg.163.com/topic/detail/12449249 https://avg.163.com/topic/detail/12449248 https://avg.163.com/topic/detail/12449246 https://avg.163.com/topic/detail/12449247 https://avg.163.com/topic/detail/12449245 https://avg.163.com/topic/detail/12449239 https://avg.163.com/topic/detail/12449243 https://avg.163.com/topic/detail/12449242 https://avg.163.com/topic/detail/12449237 https://avg.163.com/topic/detail/12449233 https://avg.163.com/topic/detail/12449231 https://avg.163.com/topic/detail/12449230 https://avg.163.com/topic/detail/12449228 https://avg.163.com/topic/detail/12448355 https://avg.163.com/topic/detail/12449227 https://avg.163.com/topic/detail/12449224 https://avg.163.com/topic/detail/12449222 https://avg.163.com/topic/detail/12449225 https://avg.163.com/topic/detail/12449220 https://avg.163.com/topic/detail/12448371 https://avg.163.com/topic/detail/12448360 https://avg.163.com/topic/detail/12448341 https://avg.163.com/topic/detail/12448430 https://avg.163.com/topic/detail/12448347 https://avg.163.com/topic/detail/12448338 https://avg.163.com/topic/detail/12448143 https://avg.163.com/topic/detail/12448331 https://avg.163.com/topic/detail/12448366 https://avg.163.com/topic/detail/12448346 https://avg.163.com/topic/detail/12449219 https://avg.163.com/topic/detail/12449218 https://avg.163.com/topic/detail/12448345 https://avg.163.com/topic/detail/12449217 123e5

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字符串（String）字面量 可以使用单引号或双引号:

"John Doe" 'John Doe'

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表达式字面量 用于计算：

5 + 6 5 * 10

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数组（Array）字面量 定义一个数组：

[40, 100, 1, 5, 25, 10]

对象（Object）字面量 定义一个对象：

{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}

函数（Function）字面量 定义一个函数：

function myFunction(a, b) { return a * b;}

JavaScript 变量

在编程语言中，变量用于存储数据值。

JavaScript 使用关键字 var 来定义变量， 使用等号来为变量赋值：

var x, length x = 5 length = 6

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变量可以通过变量名访问。在指令式语言中，变量通常是可变的。字面量是一个恒定的值。

JavaScript 操作符

JavaScript使用 算术运算符 来计算值:

(5 + 6) * 10

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JavaScript使用赋值运算符给变量赋值：

x = 5 y = 6 z = (x + y) * 10

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JavaScript语言有多种类型的运算符：

JavaScript 语句

在 HTML 中，JavaScript 语句用于向浏览器发出命令。

语句是用分号分隔：

x = 5 + 6; y = x * 10;

JavaScript 关键字

JavaScript 关键字用于标识要执行的操作。

和其他任何编程语言一样，JavaScript 保留了一些关键字为自己所用。

var 关键字告诉浏览器创建一个新的变量：

var x = 5 + 6; var y = x * 10;

JavaScript 同样保留了一些关键字，这些关键字在当前的语言版本中并没有使用，但在以后 JavaScript 扩展中会用到。

以下是 JavaScript 中最​​重要的保留关键字（按字母顺序）：