JarCastingmultiline 
Multiline strings in JavaScript
No more string concatenation or array join!
Use ES2015 template literals instead whenever possible.
Before
const str = '' +
'<!doctype html>' +
'<html>' +
' <body>' +
' <h1>❤ unicorns</h1>' +
' </body>' +
'</html>' +
'';
After
const str = multiline(()=>{/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});
How
It works by wrapping the text in a block comment, anonymous function, and a function call. The anonymous function is passed into the function call and the contents of the comment extracted.
Even though it's slower than string concat, that shouldn't realistically matter as you can still do 2 million of those a second. Convenience over micro performance always.
Install
$ npm install multiline
Usage
Everything after the first newline and before the last will be returned as seen below:
const str = multiline(()=>{/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});
Which outputs:
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
Strip indent
You can use multiline.stripIndent() to be able to indent your multiline string without preserving the redundant leading whitespace.
const str = multiline.stripIndent(()=>{/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/});
Which outputs:
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
String substitution
console.log() supports string substitution:
const str = 'unicorns';
console.log(multiline(()=>{/*
I love %s
*/}), str);
//=> 'I love unicorns'
Use cases
- CLI help output
- Test fixtures
- Queries - here an example in Cypher, the query language for Neo4j
- CLI welcome message - here in a Yeoman generator
Have one? Let me know.
Experiment
I've also done an experiment where you don't need the anonymous function. It's too fragile and slow to be practical though.
It generates a callstack and extracts the contents of the comment in the function call.
const str = multiline(/*
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/);
FAQ
But JS already has multiline strings with \?
const str = 'foo\
bar';
This is not a multiline string. It's line-continuation. It doesn't preserve newlines, which is the main reason for wanting multiline strings.
You would need to do the following:
const str = 'foo\n\
bar';
But then you could just as well concatenate:
const str = 'foo\n' +
'bar';
Browser
While it does work fine in the browser, it's mainly intended for use in Node.js. Use at your own risk.
$ npm install multiline
With Webpack, Browserify, or something similar.
Compatibility
- Latest Chrome
- Firefox >=17
- Safari >=4
- Opera >=9
- Internet Explorer >=6
Minification
Even though minifiers strip comments by default there are ways to preserve them:
- Uglify: Use
/*@preserveinstead of/*and enable thecommentsoption - Closure Compiler: Use
/*@preserveinstead of/* - YUI Compressor: Use
/*!instead of/*
You also need to add console.log after the comment so it's not removed as dead-code.
The final result would be:
const str = multiline(function(){/*!@preserve
<!doctype html>
<html>
<body>
<h1>❤ unicorns</h1>
</body>
</html>
*/console.log});
License
MIT © Sindre Sorhus