Continuing a string across a linebreak is supported in most script engines, but it is not a part of ECMAScript. Additionally, the whitespace at the beginning of each line can't be safely stripped at compile time, and any whitespace after the slash will result in tricky errors.
var myString = 'A rather long string of English text, an error message \ actually that just keeps going and going -- an error \ message to make the Energizer bunny blush (right through \ those Schwarzenegger shades)! Where was I? Oh yes, \ you\'ve got an error and all the extraneous whitespace is \ just gravy. Have a nice day.'; // Noncompliant
var myString = 'A rather long string of English text, an error message ' + 'actually that just keeps going and going -- an error ' + 'message to make the Energizer bunny blush (right through ' + 'those Schwarzenegger shades)! Where was I? Oh yes, ' + 'you\'ve got an error and all the extraneous whitespace is ' + 'just gravy. Have a nice day.';