A modern JavaScript if-elseif-else abstraction, because control flow statements are so 1995

Abstraction.js

/*
 * Abstraction.js
 *
 * Copyright (c) 2012 "Cowboy" Ben Alman
 * Licensed under the MIT license.
 * http://benalman.com/about/license/
 */

var Abstraction = (function($) {
  var _ = $.prototype;
  _.then = function(_) {
    this._[0] && !this._.slice(1).some(Boolean) && _();
    return this;
  };
  _.if = _.$if = function(_) {
    this._ = [_];
    return this.then;
  };
  _.elseif = _.$elseif = function(_) {
    this._.unshift(_);
    return this.then;
  };
  _.else = _.$else = function(_) {
    this._.some(Boolean) || _();
    return this;
  };
  return $;
}(function() {
  this.then = this.then.bind(this);
  this.then.then = this.then;
}));

syntax1.js

// Working on the "chain" gang

(new Abstraction)

  .if(true).then(function() {
    console.log('log 1');
  })

  .if(false).then(function() {
    console.log('no log');
  })

  .if(true).then(function() {
    console.log('log 2');
  })
  .else(function() {
    console.log('no log');
  })

  .if(false).then(function() {
    console.log('no log');
  })
  .else(function() {
    console.log('log 3');
  })

  .if(true).then(function() {
    console.log('log 4');
  })
  .elseif(true).then(function() {
    console.log('no log');
  })
  .else(function() {
    console.log('no log');
  })

  // You actually don't even need the .then!
  .if (false) (function() {
    console.log('no log');
  })
  .elseif (true) (function() {
    console.log('log 5');
  })
  .else (function() {
    console.log('no log');
  });

syntax2.js

// For the sake of this example looking totally insane, this function returns the
// console.log function with all arguments pre-applied, to be called at a later time.

function console$log() {
  return Function.bind.apply(console.log, [console].concat([].slice.call(arguments)));
}

// Dolla dolla "with" y'all (aka WTF)

with (new Abstraction) {

  $if (true) (
    console$log('log 1')
  )

  $if (false) (
    console$log('no log')
  )

  $if (true) (
    console$log('log 2')
  )
  $else (
    console$log('no log')
  )

  $if (false) (
    console$log('no log')
  )
  $else (
    console$log('log 3')
  )

  $if (true) (
    console$log('log 4')
  )
  $elseif (true) (
    console$log('no log')
  )
  $else (
    console$log('no log')
  )

  $if (false) (
    console$log('no log')
  )
  $elseif (true) (
    console$log('log 5')
  )
  $else (
    console$log('no log')
  )

}

Also see the other version, Abstraction.js "Lite".