属性只有一个值的这类 html 属性是怎么回事，该如何设置值；比如：checked = “checked” vs checked = true

参考链接：https://stackoverflow.com/questions/10650233/checked-checked-vs-checked-true

问：

 What is the difference between the below two usages?
 
 document.getElementById('myRadio').checked = "checked";
 and
 
 document.getElementById('myRadio').checked = true;
 For me, both are behaving the same way. But, I am just curious to know why there exist two methods to do the same.
 
 Which one will be the ideal usage? I need to support IE7 and higher versions.

答：

 document.getElementById('myRadio').checked is a boolean value. It should be true or false
 
 document.getElementById('myRadio').checked = "checked"; casts the string to a boolean, which is true.
 
 document.getElementById('myRadio').checked = true; just assigns true without casting.
 
 Use true as it is marginally more efficient and is more intention revealing to maintainers.

document.getElementById（'myRadio'）。checked是一个布尔值。 这应该是真的或假的

document.getElementById（'myRadio'）。checked =“checked”; 将字符串转换为布尔值，这是正确的。

document.getElementById（'myRadio'）。checked = true; 只是分配true而不投射。

使用true，因为它的效率稍微高一点，而且更有意向维护者展示。

所以设置这种单属性的值为 true 或 false 就对了。