How can I use js eval to return a value?

The first method is to delete return keywords and the semicolon:

var expression = '2+2+2';
var result = eval('(' + expression + ')')
alert(result);

note the ‘(‘ and ‘)’ is a must.

or you can make it a function:

var expression = 'return 2+2+2;'
var result = eval('(function() {' + expression + '}())');
alert(result);

even simpler, do not use eval:

var expression = 'return 2+2+2;';
var result = new Function(expression)();
alert(result);