javascript是否在布尔表达式中使用优化？ [英] Does javascript use optimization in boolean expressions?

问题描述

当我决定用经典的javascript构建普通的web表单验证时，我有一个奇怪的错误。输入文本字段有几个onblur处理程序和一个form-submit处理程序。

I have strange error when I decided to build ordinary web-form validation with classic javascript. There are several "onblur" handlers for input text fields and one "form-submit" handler.

当我这样使用它们时：

function loginCheck() {
  ... return true of false 
}

function passwordCheck() { 
   ...
}

function formValidation() {
  return loginCheck() && passwordCheck();
}

它无法正常工作：passwordCheck从未调用过loginCheck失败了！

It doesn't work as I expect: "passwordCheck" never called if loginCheck is failed!

最后我有解决方法

function formValidation() {
  ok = loginCheck();
  ok &= passwordCheck();
  return ok;
}

现在执行密码检查。但是当我选择：

Now password check is executed. But when I choose:

function formValidation() {
      ok = loginCheck();
      ok = ok && passwordCheck();
      return ok;
    }

如果loginCheck失败，则不会再次调用passwordCheck。

passwordCheck is never called again if loginCheck failed.

此外：loginCheck& passwordCheck返回布尔值，但& =运算符将其转换为0或1。 0对我的 onsubmit =return checkForm处理程序不起作用。我必须再次将我的& =结果转换为布尔值：

Moreover: loginCheck & passwordCheck return boolean values, but &= operator covert it to "0" or "1". "0" doesn't work for my onsubmit="return checkForm" handler. I have to convert my &= result to boolean once again:

function formValidation() {
      ok = loginCheck();
      ok &= passwordCheck();
      return ok != 0;
    }

这是javascript引擎的正常行为吗？

It is a normal behavior for javascript engines ?

推荐答案

是的，这很正常。它被称为短路评估，既方便又常见（即存在于很多语言（C，C ++，Java，Perl，许多其他语言），而不仅仅是JavaScript）。

Yes, it's normal. It's called a short-circuit evaluation and is both handy and very common (i.e. is present in a lot of languages (C, C++, Java, Perl, many others), not just JavaScript).

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