Pregunta ¿Por qué no son ◎ ܫ ◎ y nombres válidos de JavaScript?


Noté que en Internet Explorer (pero, desafortunadamente, no en los otros navegadores que probé), puedes usar algunos nombres de variables Unicode. Esto me alegraba el día y estaba encantado de poder escribir un código Unicode cargado así:

var ктоείναι草泥马 = "You dirty horse.",
    happynmatpeia = ":)Yay!",
    ಠ_ಠ = "emoticon";

alert(ктоείναι草泥马 + happynmatpeia + ಠ_ಠ);

Por alguna razón, sin embargo, ◎ܫ◎, _ y  no son nombres de variable válidos

Por qué ಠ_ಠ y 草泥马 trabajo, pero ◎ܫ◎, _ y  no?

EDITAR: Pruébelo en su navegador en JSFiddle. Lo probé en Internet Explorer 9, Chrome, Firefox y Opera. Hasta ahora, parece que solo funciona en Internet Explorer 9. (No sé sobre Internet Explorer 8 y abajo). Avíseme si funciona en otro navegador.


696
2017-09-17 00:05


origen


Respuestas:


ಠ_ಠ y 草泥 马 solo contienen "letras" usadas en alfabetos reales; es decir, ಠ es un símbolo del Alfabeto Kannaday 草泥 马 consiste en caracteres chinos.

◎ y, sin embargo, son puramente símbolos; no están asociados con ningún alfabeto.

los Estándar ECMAScript, capítulo 7.6 (que todos los navegadores excepto Internet Explorer están siguiendo), establece que un identificador debe comenzar con uno de los siguientes.

  • una carta Unicode
  • $ o _
  • \ seguido por una secuencia de escape unicode.

Los siguientes caracteres de un identificador deben ser uno de los siguientes.

  • cualquiera de los personajes permitidos al comienzo
  • una marca de combinación Unicode
  • un dígito Unicode
  • una puntuación de conector Unicode
  • un cero-ancho-no-carpintero
  • un carpintero de ancho cero

IE va más allá del estándar y es lo suficientemente permisivo como para permitir algunos símbolos, como.

Hay una herramienta eso le dirá si alguna cadena que ingrese es un nombre de variable de JavaScript válido de acuerdo con ECMAScript 5.1 y Unicode 6.1.


583
2017-09-17 00:15



EcmaScript 262, sección 7.6 dice que los nombres deben comenzar con $, _, o una letra Unicode, y después pueden contener esos caracteres, o marcas de combinación Unicode, dígitos Unicode o puntuación del conector Unicode (y un par de caracteres de control de formato que son específicos del idioma).

Entonces, la diferencia entre los identificadores permitidos y no permitidos en sus casos es probablemente si el personaje principal se considera una "letra".


79
2017-09-17 00:13



Citar Nombres válidos de las variables de JavaScript, mi reseña que resume las secciones de especificaciones relevantes:

Un identificador debe comenzar con $, _, o cualquier personaje en las categorías Unicode "Letra mayúscula (Lu)", "Letra minúscula (Ll)", "Carta de Titlecase (Lt)", "Letra modificadora (Lm)", "Otra carta (Lo)", o "Número de letra (Nl)".

El resto de la cadena puede contener los mismos caracteres, más cualquier U + 200C de ancho cero sin unión caracteres, Carpintero de ancho cero U + 200D personajes y personajes en las categorías Unicode "Marca no espaciadora (Mn)", "Marca de combinación de espaciado (Mc)", "Número de dígito decimal (Nd)", o "Puntuación del conector (Pc)".

También he creado una herramienta eso le dirá si alguna cadena que ingrese es un nombre de variable de JavaScript válido de acuerdo con ECMAScript 5.1 y Unicode 6.3:

JavaScript variable name validator


PD Si tuviera que resumir todas estas reglas en una sola expresión regular única de ASCII para JavaScript, Tendría más de 9,000 caracteres de largo. Aquí está:

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43
2018-02-18 00:22



Por la gran justicia: como la mayoría de las cosas en JS son "objetos", puede usar sintaxis de corchetes cuadrados:

window["◎ܫ◎"] = true;
alert(window["◎ܫ◎"]); // alerts "true"

Esto es lo mismo que var smth = true en contexto global.


10
2018-04-10 12:49