Complementary function to util.format() in Node.js

Question

I know how to format a string using %f, %d etc. using util.format(). Can someone tell me which is the complementary function that enables SCANNING from a string (not from console input).

For example:

Running...

const util = require('util');
var weatherStr = util.format(`The temperature at %d o' clock was %f deg. C and the humidity was %f.`, 5, 23.9, 0.5);
console.log(weatherStr);

...generates...

The temperature at 5 o' clock was 23.9 deg. C and the humidity was 0.5.

I was expecting a util function which would work such that running the following code...

const util = require('util');
var weatherStr = 'The temperature at 5 o' clock was 23.9 deg. C and the humidity was 0.5.';
console.log(util.????(tempStr, `humidity was %f.`));

...generates...

0.5

Which is the util function that does this? I don't think "parseFloat" will work because it will extract 23.9.

I'm new to JS and Node but I expected a "scan" function. I know there is a scanf npm library but it seems to work with console input rather than existing strings. I have been doing searches for "%f" among JS and Node functions and surprisingly util.format seems to be the only one with a mention of it.

Answer 1

I don't know of any scan library like that, but you can use regular expressions. Here are some patterns you could use:

• Integer: [+-]?\\d+
• Decimal: [+-]?\\d+(?:\\.\\d+)?

If you put these in a capture group, you can access the corresponding matches from the array that String#match returns:

 var weatherStr = "The temperature at 5 o'clock was 23.9 deg. C and the humidity was 0.5."; console.log(+weatherStr.match(/humidity was ([+-]?\\d+(?:\\.\\d+)?)./)[1]); 

You could create a utility function that can deal with %d and %f :

 function scanf(input, find) { var pattern = { "d": "(\\\\d+)", "f": "(\\\\d+(?:\\\\.\\\\d+)?)" }; find = find // Escape characters for use in RegExp constructor: .replace(/[-\\/\\\\^$*+?.()|[\\]{}]/g, '\\\\$&') // Replace %-patterns .replace(/((?:\\\\)*)%([az])/g, function (m, a, b) { return a.length % 4 == 0 && b in pattern ? a + pattern[b] : m; }); var match = input.match(new RegExp(find)); return match && match.slice(1).map(Number); } var weatherStr = "The temperature at 5 o'clock was 23.9 deg. C and the humidity was 0.5."; console.log(scanf(weatherStr, "humidity was %f")); console.log(scanf(weatherStr, "at %d o'clock was %f")); 

Answer 2

Thanks trincot!

Actually it turns out the scanf npm library ( https://www.npmjs.com/package/scanf ) DOES solve my problem. I just hadn't read it all the way through. I had to install "sscanf" (note the double-s) as well. The sscanf method (listed at the bottom of the package page) works just as I expected.

I'm surprised this package is not more popular, but it is what I need. Thanks again!