an in window and "a" in window?
an in window and "a" in window?
the first is a variable and the second is a string
the first value of the is an attribute of variable a window , and the second is whether the string "a" is an attribute of window :
A without quotation marks is a variable, then an in window can be a judgment statement or an assignment statement after for.
while "a" is a string constant, "a" in window can only be a judgment statement.
take a look at the document. Portal
emphasizes the situation of prop in prop in object :
an attribute name or array index of type symbol (non-symbol types will be forced to string).
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