replace-tokens.js

index.js

// `replaceTokens` is a modification of Crockford's `String.prototype.supplant`
// which takes works on an object/array (if given as the second argument)
// or a variable number of replacements.
module.exports = function replaceTokens (tmpl/*, replacements... */) {
  var args = [].slice.call(arguments, 1);
  if (args[0] != null && (Array.isArray(args[0]) || typeof args[0] === 'object')) {
    args = args[0];
  }
  return tmpl.replace(/\{([^{}]*)\}/g, function (match, index) {
    var result = args[index];
    return typeof result === 'string' || typeof result === 'number' ? result : match;
  });
};

package.json

{
  "name": "replace-tokens",
  "version": "0.0.0",
  "description": "A .NET-style token replacer for strings",
  "main": "index.js",
  "scripts": {
    "test": "tape test.js"
  },
  "author": "Leroy Campbell <leroy@artisonian.com>",
  "license": "MIT",
  "devDependencies": {
    "tape": "^2.13.3"
  }
}

test.js

var test = require('tape');
var replace = require('./index');

test('replacing tokens in numeric order', function (t) {
  t.plan(1);

  var tmpl = 'The {0} walks {1} to the {2}.';
  var result = replace(tmpl, 'fox', 'quickly', 'fence');

  t.equal(result, 'The fox walks quickly to the fence.');
});

test('replacing tokens out of numeric order', function (t) {
  t.plan(1);

  var tmpl = "If you're {2} and you know it, {0} your {1}.";
  var result = replace(tmpl, 'happy', 'clap', 'hands');

  t.equal(result, "If you're hands and you know it, happy your clap.");
});

test('using only the given replacements', function (t) {
  t.plan(4);

  var tmpl = 'Do not {0} the {1}.';

  t.equal(replace(tmpl), 'Do not {0} the {1}.');
  t.equal(replace(tmpl, 'touch'), 'Do not touch the {1}.');
  t.equal(replace(tmpl, null, 'cookie'), 'Do not {0} the cookie.');
  t.equal(replace(tmpl, 'touch', 'cookie', 'at all'), 'Do not touch the cookie.');
});

test('using a replacement more than once', function (t) {
  t.plan(1);

  var tmpl = 'You put your {0} {1} in, you put your {0} {1} out...';
  var result = replace(tmpl, 'left', 'foot');

  t.equal(result, 'You put your left foot in, you put your left foot out...');
});

test('using an array for replacements', function (t) {
  t.plan(3);

  var tmpl = 'The {0} part of waking up is {1} in your {2}.';
  t.equal(replace(tmpl, ['best']), 'The best part of waking up is {1} in your {2}.');
  t.equal(replace(tmpl, ['best', 'Folgers']), 'The best part of waking up is Folgers in your {2}.');
  t.equal(replace(tmpl, ['best', 'Folgers', 'cup']), 'The best part of waking up is Folgers in your cup.');
});

test('using an object for replacements', function (t) {
  t.plan(2);

  var tmpl = 'The {thing} on the bus go {action} and {action}.';
  var result = replace(tmpl, { thing: 'wheels', action: 'round' });
  t.equal(result, 'The wheels on the bus go round and round.');

  tmpl = '{name} the {0} has {count} {1}.';
  result = replace(tmpl, { 0: 'camel', 1: 'humps', name: 'Sally', count: 'five' });
  t.equal(result, 'Sally the camel has five humps.');
});