var mystring = "hello \
I found it because I was trying to test something with a string that was coming over ajax split across multiple lines and I wanted to test a static string with the same space and tab characters in it.
I think this is quite handy if you want to create a big long bit of HTML. I find it a bit more readable than having lots of plus signs all through the code:
myElement.innerHTML = " \
<li>First item</li> \
<li>Second item</li> \
<li>Third item</li> \
It’s not part of the EMCAScript standard. It’s something the browsers support for backwards compatibility. I guess that means it’s possible it could one day be deprecated. That’s a bit of a pity because I think it’s quite useful for making string concat easier to read.