为什么Javascript` if ... else if`不以`else`结尾？ [英] Why would Javascript `if...else if` not end with an `else`?

问题描述

以下是我正在使用的教程中的JavaScript代码片段。我不明白为什么它不以最终的 else 子句结束;我认为这是一条规则。

  var curScene = 0; 
 
函数changeScene（决定）{
 var message =; 
 
 if（curScene == 1）{
 message =welcome; 
}否则如果（curScene == 2）{
 message =这是场景二; 
}否则如果（curScene == 3）{
 message =这是场景三; 
} 
 
 document.getElementById（sceneimg）。src =scene+ curScene +。png; 
 
 if（message！=）{
 alert（message）; 
} 
} 
  

解决方案

我以为它总是应该以else结束？

你错了。 else 块是可选的。如果没有否则 $ b $

Here is a snippet of JavaScript code from a tutorial I was working with. I don’t understand why it doesn’t end with a final else clause; I thought that was a rule.

var curScene = 0;

function changeScene(decision) {
  var message = "";

  if(curScene == 1) {
    message = " welcome";
  } else if (curScene == 2) {
    message = " this is scene two";
  } else if (curScene == 3) {
    message = " this is scene three";
  }

  document.getElementById("sceneimg").src = "scene" + curScene + ".png";

  if(message != ""){
    alert(message);
  }
}

解决方案

I thought it was always supposed to end with an "else"?

You are mistaken. The else block is optional. You can have if without else.

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