CodeWars: CamelCase Method

CodeWars: CamelCase Method.txt

ASSIGNMENT
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Write simple .camelCase method (camel_case function in PHP, CamelCase in C# or camelCase in Java) for strings. 
All words must have their first letter capitalized without spaces.

For instance:

"hello case".camelCase() => HelloCase
"camel case word".camelCase() => CamelCaseWord

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SOLUTION
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String.prototype.camelCase = function(){  
  return this.split(' ').map((word) => word.charAt(0).toUpperCase() + word.slice(1))
                        .join('');
}; 
'test case'.camelCase();

good job

Hi Can I know why did u use "+" sign before slice ? thanks