Thunk-Switch.js

var Switch = function(expr){
        return new YetSucceed(expr);
}
 
var Succeed = { case : function(cond,proc){ return this; } };
 
var YetSucceed = function(expr){ this.expr = expr; };
YetSucceed.prototype.case = function(cond, proc){
    if(cond() === this.expr){
        proc();
        return Succeed;
    }
    return this;
}
 
var x = 0;
 
new Switch(true).
        case(function(){ return x > 0; }, 
             function(){
              console.log(x + " is positive.");
        }).
        case(function(){ return x === 0; }, 
             function(){
                console.log(x + " is zero. ");
        }).
        case(function(){ return x < 0; },
             function(){
            console.log(x + " is negative . ");
        });