More on JavaScript Operators
String operators
In addition to the comparison operators, which can be used on string values, the concatenation operator (+) concatenates two string values together, returning another string that is the union of the two operand strings.
For example,
console.log('my ' + 'string'); // console logs the string "my string".
The shorthand assignment operator += can also be used to concatenate strings.
For example,
var mystring = 'alpha'; mystring += 'bet'; // evaluates to "alphabet" and assigns this value to mystring.