javascript

Chapter 18: Advanced Techniques
In this example, a curried version of add() is created that has the first argument bound to 5. When
curriedAdd() is called and 3 is passed in, the 3 becomes the second argument of add() , while the first
is still 5, resulting in the sum of 8. You can also provide all function arguments as shown in this example:
function add(num1, num2){
return num1 + num2;
}
var curriedAdd = curry(add, 5, 12);
alert(curriedAdd()); //17
Here, the curried add() function provides both arguments, so there ’ s no need to pass them in later.
Function currying is often included as part of function binding, creating a more complex bind()
function. For example:
function bind(fn, context){
var args = Array.prototype.slice.call(arguments, 2);
return function(){
var innerArgs = Array.prototype.slice.call(arguments);
var finalArgs = args.concat(innerArgs);
return fn.apply(context, finalArgs);
};
}
The major changes from the curry() function are the number of arguments passed in to the function
and how that affects the result of the code. Whereas curry() simply accepts a function to wrap, bind()
accepts the function and a context object. That means the arguments for the bound function start at the
third argument instead of the second, which changes the first call to slice() . The only other change is
to pass in the context object to apply() on the third - to - last line. When bind() is used, it returns a
function that is bound to the given context and may have some number of its arguments set already. This
can be useful when you want to pass arguments in to an event handler in addition to the event object,
such as this.
var handler = {
message: “Event handled”,
};
handleClick: function(name, event){
alert(this.message + “:” + name + “:” + event.type);
}
var btn = document.getElementById(“my-btn”);
EventUtil.addHandler(btn, “click”, bind(handler.handleClick, handler, “my-btn”));
In this updated example, the handler.handleClick() method accepts two arguments: the name of the
element that you ’ re working with and the event object. The name is passed in to the bind() function as
the third argument and then gets passed through to handler.handleClick() , which also receives the
event object.
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