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[javascript] toClosure
Posted by Erik on Jan 20 2006 @ 15:48 :: 3851 unique visits
My post from yesterday contained an interresting toClosure function. I have improved this function a little to allow for more interresting usages such as event handlers:CODE: JAVASCRIPT
Function.prototype.toClosure = function() {
var f = this;
// a Array object is needed because arguments doesn't support concat/join.
var a = new Array(arguments.length);
for (var i = 0; i < arguments.length; ++i) {
a[i] = arguments[i];
}
return function() {
// concat/join the 2 argument array's
for (var i = 0; i < arguments.length; ++i) {
a[a.length] = arguments[i];
}
return f.apply(this, a);
}
}
var f = this;
// a Array object is needed because arguments doesn't support concat/join.
var a = new Array(arguments.length);
for (var i = 0; i < arguments.length; ++i) {
a[i] = arguments[i];
}
return function() {
// concat/join the 2 argument array's
for (var i = 0; i < arguments.length; ++i) {
a[a.length] = arguments[i];
}
return f.apply(this, a);
}
}
One simple example:
CODE: JAVASCRIPT
function add(i, j) {
return i + j;
}
var plus2 = add.toClosure(2);
plus2(3); // will return 5 (add(2, 3))
return i + j;
}
var plus2 = add.toClosure(2);
plus2(3); // will return 5 (add(2, 3))
A simple example even handler:
CODE: JAVASCRIPT
// str is the argument given at the time the closure was created
// e is the event objects which good browsers pass to the onclick handler
function foo(str, e) {
// do something with the event
var button = e ? e.button : window.event.button; // for IE
// the this keyword point to the right object so this.href works
alert(this.href + str + button);
return false; // don't follow the link
}
var somelink = document.getElementById('somelink');
somelink.onclick = foo.toClosure('\n foo \n');
// e is the event objects which good browsers pass to the onclick handler
function foo(str, e) {
// do something with the event
var button = e ? e.button : window.event.button; // for IE
// the this keyword point to the right object so this.href works
alert(this.href + str + button);
return false; // don't follow the link
}
var somelink = document.getElementById('somelink');
somelink.onclick = foo.toClosure('\n foo \n');
8 comments posted so far
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3. On Mar 10 2006 @ 01:42 url wrote:
here is a good article about currying with javascript :http://www.svendtofte.com/code/curried_javascript/
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1. On Jan 20 2006 @ 17:15 l0ne wrote:
Partially applying arguments to a function, yielding a new function, is called currying in functional languages... if I'm not mistaken.