September 2024
Intermediate to advanced
706 pages
22h 41m
Spanish
Content preview from JavaScript: La Guía Definitiva, 7ª Edición
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Capítulo 5. Declaraciones
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Enel capítulo 4 se describieron las expresiones como frases de JavaScript. Por esa analogía, las sentencias son frases o comandos de JavaScript. Al igual que las frases en inglés se terminan y separan entre sí con puntos, las sentencias en JavaScript se terminan con punto y coma(§2.6). Las expresiones se evalúan para producir un valor, pero las sentencias se ejecutan para que ocurra algo.
Una forma de "hacer que ocurra algo" es evaluar una expresión que tenga efectos secundarios. Las expresiones con efectos secundarios, como las asignaciones y las invocaciones de funciones, pueden funcionar por sí solas como sentencias, y cuando se utilizan de este modo se conocen como sentencias de expresión. Una categoría similar de sentencias son las sentencias de declaración que declaran nuevas variables y definen nuevas funciones.
Los programas JavaScript no son más que una secuencia de sentencias a ejecutar. Por defecto, el intérprete de JavaScript ejecuta estas sentencias una tras otra en el orden en que están escritas. Otra forma de "hacer que ocurra algo" es alterar este orden de ejecución por defecto, y JavaScript tiene una serie de sentencias o estructuras de control que hacen precisamente esto:
- Condicionales
-
Sentencias como
ifyswitchque hacen que el intérprete de JavaScript ejecute u omita otras sentencias en función del valor de una expresión ...
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