Why is this result? what is the difference between the directly declared string and new"s? why is the string of s new checked with instanceof, that is, Object and String?
Why is this result? what is the difference between the directly declared string and new"s? why is the string of s new checked with instanceof, that is, Object and String?
what's the difference between a directly declared string and a new
one is a literal string
one is an instance of String type, and valueOf returns a literal string, so 'a'! = = new String ('a') , but 'a' = = new String ('a') , 'a' = new String ('a'). ValueOf ()
Why is the string of s new checked withinstanceof, that is,ObjectandString?
because String inherits from Object , String instanceof Object
remember the JS prototype chain mechanism? The string that comes out through new String inherits the String object, and String inherits the Object object, so the following s instance Object | String is true. There are two data types: value type and reference type in
JS. S created by literals is directly assigned to the value 'hello', so it belongs to the value type.' hello' is an ordinary constant that does not inherit from any object, so s instance Object is false.
note that among the underlying types, only number boolean string can be passed by value, var obj = {}; is still a reference type.
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