JavaScript contains a number of built-in functions and also 
        allows you to create your own functions. Some examples of built in functions 
        are: 
        
      ·        
        alert(): This function is used to display messages, variables, or numbers 
        to user in a rectangular window that has OK button in it. 
      ·        
        Confirm():This function is quite similar to the alert function. However 
        it shows two buttons OK and Cancel and allows the user to make a decision. 
      ·        
        toString(): This function returns the string representation of the number’s 
        value. 
      ·        
        valueOf(): This function returns the number’s value. 
      ·        
        Length(): This function returns the length of a string. 
      ·        
        indexOf(): This function returns the index within the calling string object 
        of the first occurrence of the specified value. It returns -1 if the value 
        is not found 
  
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