Why “foo”.toString() is not the same as toString.call(“foo”)?

Question

Here is a question in JavaScript below:

// Tested via Google Chrome console.
var toString = Object.prototype.toString;

"foo".toString(); // "f         


        

Answer 1

String.prototype.toString overrides Object.prototype.toString. They are not the same function.

From the specification of String.prototype.toString:

Returns this String value. (Note that, for a String object, the toString method happens to return the same thing as the valueOf method.)

And Object.prototype.toString:

When the toString method is called, the following steps are taken:

1. Let O be the result of calling ToObject passing the this value as the argument.
2. Let class be the value of the [[Class]] internal property of O.
3. Return the String value that is the result of concatenating the three Strings "[object ", class, and "]".

Arrays behave similar, they also override toString():

> [1,2].toString()
  "1,2"