String.prototype.valueOf()
  The valueOf() method returns the primitive value of a
  String object.
Syntax
valueOf()
Return value
A string representing the primitive value of a given String object.
Description
  The valueOf() method of String returns the primitive value
  of a String object as a string data type. This value is equivalent to
  String.prototype.toString().
This method is usually called internally by JavaScript and not explicitly in code.
Examples
Using valueOf()
var x = new String('Hello world');
console.log(x.valueOf()); // Displays 'Hello world'
Specifications
| Specification | 
|---|
| ECMAScript Language Specification # sec-string.prototype.valueof | 
Browser compatibility
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