Use of String.Format in JavaScript?

Question

This is driving me nuts. I believe I asked this exact same question, but I can\'t find it any more (I used Stack Overflow search, Google Search, manually searched my po

Answer 1

Use a template literal in ECMAScript 6:

var customer = { name: "Foo" }
var card = { amount: 7, product: "Bar", unitprice: 42 }
var message = `Hello ${customer.name},
               want to buy ${card.amount} ${card.product} for
               a total of ${card.amount * card.unitprice} bucks?`

Answer 2

Here's a solution that just works with String.prototype:

String.prototype.format = function() {
    var s = this;
    for (var i = 0; i < arguments.length; i++) {       
        var reg = new RegExp("\\{" + i + "\\}", "gm");             
        s = s.replace(reg, arguments[i]);
    }
    return s;
}

Answer 3

Here are my two cents:

function stringFormat(str) {
  if (str !== undefined && str !== null) {
    str = String(str);
    if (str.trim() !== "") {
      var args = arguments;
      return str.replace(/(\{[^}]+\})/g, function(match) {
        var n = +match.slice(1, -1);
        if (n >= 0 && n < args.length - 1) {
          var a = args[n + 1];
          return (a !== undefined && a !== null) ? String(a) : "";
        }
        return match;
      });
    }
  }
  return "";
}

alert(stringFormat("{1}, {0}. You're looking {2} today.",
  "Dave", "Hello", Math.random() > 0.5 ? "well" : "good"));

Answer 4

Based on @roydukkey's answer, a bit more optimized for runtime (it caches the regexes):

(function () {
    if (!String.prototype.format) {
        var regexes = {};
        String.prototype.format = function (parameters) {
            for (var formatMessage = this, args = arguments, i = args.length; --i >= 0;)
                formatMessage = formatMessage.replace(regexes[i] || (regexes[i] = RegExp("\\{" + (i) + "\\}", "gm")), args[i]);
            return formatMessage;
        };
        if (!String.format) {
            String.format = function (formatMessage, params) {
                for (var args = arguments, i = args.length; --i;)
                    formatMessage = formatMessage.replace(regexes[i - 1] || (regexes[i - 1] = RegExp("\\{" + (i - 1) + "\\}", "gm")), args[i]);
                return formatMessage;
            };
        }
    }
})();

Answer 5

if (!String.prototype.format) {
    String.prototype.format = function () {
        var args = arguments;
        return this.replace(/{(\d+)}/g, function (match, number) {
            return typeof args[number] != 'undefined'
              ? args[number]
              : match
            ;
        });
    };
}

Usage:

'{0}-{1}'.format('a','b');
// Result: 'a-b'

JSFiddle

Answer 6

You can do series of replaces like that:

function format(str)
{
    for(i = 1; i < arguments.length; i++)
    {
        str = str.replace('{' + (i - 1) + '}', arguments[i]);
    }
    return str;
}

Better approach will be to use replace with function parameter:

function format(str, obj) {
    return str.replace(/\{\s*([^}\s]+)\s*\}/g, function(m, p1, offset, string) {
        return obj[p1]
    })
}

This way you can provide both indices and named parameters:

var arr = ['0000', '1111', '2222']

arr.a = 'aaaa'

str = format(" { 0 } , {1}, { 2}, {a}", arr)
// returns 0000 , 1111, 2222, aaaa