Splitting a long string literal over multiple lines can often aid readability, but this also makes it difficult to notice whether a space is missing where the strings are concatenated.

Check the string literal to see whether it has the intended text. In particular, look for missing spaces near line breaks.

The following example shows a text literal that is split over two lines and omits a space character between the two words at the line break.

Mozilla Developer Network: Strings: Long literal strings.