在 JavaScript 中。如何判断对象内部是否存在字段？
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In Javascript. how can I tell if a field exists inside an object?
提问by Khoi
And of course I want to do this code-wise. It's not that there isn't alternative to this problem I'm facing, just curious.
当然，我想在代码方面做这个。并不是说我面临的这个问题没有替代方案，只是好奇。
采纳答案by Peter Kruithof
UPDATE: use the hasOwnPropertymethod as Gary Chambers suggests. The solution below will work, but it's considered best practice to use hasOwnProperty.
更新：使用hasOwnPropertyGary Chambers 建议的方法。下面的解决方案将起作用，但它被认为是使用hasOwnProperty.
if ('field' in obj) {
}
回答by Gary Chambers
This will ignore attributes passed down through the prototype chain.
这将忽略通过原型链向下传递的属性。
if(obj.hasOwnProperty('field'))
{
// Do something
}
回答by Eugene Ilyushin
In addition to the above, you can use following way:
除上述方法外，您还可以使用以下方式：
if(obj.myProperty !== undefined) {
}
回答by Aliaksandr Sushkevich
回答by will
After much frustration trying to test a field name which is passed via a variable, I came up with this:
在尝试测试通过变量传递的字段名称时非常沮丧，我想出了这个：
`function isset(fName){
try{
document.getElementById(fName).value=document.getElementById(fName).value;
return true;
}catch(err){
return false;
}
}
`
`
The function uses the try/catch function of javascript - if it can't set the field value it will trigger an error which is caught and passed back as false, otherwise true is returned.
该函数使用 javascript 的 try/catch 函数 - 如果它无法设置字段值，它将触发一个错误，该错误被捕获并作为 false 传回，否则返回 true。
