当涉及对象字面量时，JavaScript是否提起if语句？ [英] Does JavaScript hoist if statements when object literals are involved?

问题描述

  var foo = {}; document.body.innerHTML = console.log = location.hash ='Hi'+'< br> '+ foo.bar +'< br> '+ foo.baz; setTimeout（function（）{foo.baz = foo [bar] = []; foo.bar.push（new Date）; foo.baz.push（new Date）; document.body.innerHTML = console.log = location.hash ='Hi'+'< br>'+ foo.bar +'< br>'+ foo.baz}，5000）;  

node.bar

解决方案

等于 false ，（node.foo&&& node.bar）将求值为 false 是否附加属性。不要检查这些属性是否 true ，您应该检查它们是否未定义：

  if（typeof node.foo！=='undefined'&&&typeof node.bar！=='undefined'）
 {
 ... 
} 
 else 
 {
 ... 
} 
  

var foo = {}; document.body.innerHTML = console.log = location.hash = 'Hi ' + '<br>  ' + foo.bar + '<br>  ' + foo.baz; setTimeout(function(){foo.baz = foo["bar"] = []; foo.bar.push(new Date); foo.baz.push(new Date); document.body.innerHTML = console.log = location.hash = 'Hi ' + '<br>  ' + foo.bar + '<br>  ' + foo.baz}, 5000);

解决方案

Since you set node.bar equal to false, (node.foo && node.bar) will evaluate to false whether the properties are attached or not. Rather than checking if those properties are true, you should check whether they are undefined:

if (typeof node.foo !== 'undefined' && typeof node.bar !== 'undefined') 
{ 
  ...
} 
else 
{
  ...
}

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