JavaScript equivalent to printf/String.Format

Question

I'm looking for a good JavaScript equivalent of the C/PHP printf() or for C#/Java programmers, String.Format() (IFormatProvider for .NET).

My basic requirement is a thousand separator format for numbers for now, but something that handles lots of combinations (including dates) would be good.

I realize Microsoft's Ajax library provides a version of String.Format(), but we don't want the entire overhead of that framework.

Answer 1

Just in case someone needs a function to prevent polluting global scope, here is the function that does the same:

  function _format (str, arr) {
    return str.replace(/{(\d+)}/g, function (match, number) {
      return typeof arr[number] != 'undefined' ? arr[number] : match;
    });
  };

Answer 2

I use this simple function:

String.prototype.format = function() {
    var formatted = this;
    for( var arg in arguments ) {
        formatted = formatted.replace("{" + arg + "}", arguments[arg]);
    }
    return formatted;
};

That's very similar to string.format:

"{0} is dead, but {1} is alive!".format("ASP", "ASP.NET")

Answer 3

Edit: From ES6 on you could use template strings:

let soMany = 10;
console.log(`This is ${soMany} times easier!`);
// "This is 10 times easier!

See Kim's answer below for details.

Original answer:

Try sprintf() for JavaScript.

---

Update    Ok, if you really want to do a simple format method on your own, don’t do the replacements successively but do them simultaneously.

Because most of the other proposals that are mentioned fail when a replace string of previous replacement does also contain a format sequence like this:

"{0}{1}".format("{1}", "{0}")

Normally you would expect the output to be {1}{0} but the actual output is {1}{1}. So do a simultaneously replacement instead like in fearphage’s suggestion.

Answer 4

jsxt, Zippo

This option fits better.

String.prototype.format = function() {
    var formatted = this;
    for (var i = 0; i < arguments.length; i++) {
        var regexp = new RegExp('\\{'+i+'\\}', 'gi');
        formatted = formatted.replace(regexp, arguments[i]);
    }
    return formatted;
};

With this option I can replace strings like these:

'The {0} is dead. Don\'t code {0}. Code {1} that is open source!'.format('ASP', 'PHP');

With your code the second {0} wouldn't be replaced. ;)

Answer 5

JavaScript programmers can use String.prototype.sprintf at https://github.com/ildar-shaimordanov/jsxt/blob/master/js/String.js. Below is example:

var d = new Date();
var dateStr = '%02d:%02d:%02d'.sprintf(
    d.getHours(), 
    d.getMinutes(), 
    d.getSeconds());

Answer 6

The PHPJS project has written JavaScript implementations for many of PHP's functions. Since PHP's sprintf() function is basically the same as C's printf(), their JavaScript implementation of it should satisfy your needs.