One of the new feature in jQuery 1.4 is setter function. For a while now, you’ve been able to pass a function into .attr() and the return value of that function is set into the appropriate attribute. This functionalilty has now been extended into all setter methods: .css(), .attr(), .val(), .html(), .text(), .append(), .prepend(), .before(), .after(), .replaceWith(), .wrap(), .wrapInner(), .offset(), .addClass(), .removeClass(), and .toggleClass(). Addtionally, for the following options, the current value of the item is passed into the function as the second argument: .css(), .attr(), .val(), .html(), .text(), .append(), .prepend(), .offset(), .addClass(), .removeClass(), and .toggleClass().
$('a[target]').attr("title", function(i, currentValue){
return currentValue+ " (Opens in External Window)";
});
$("#xx").text(function (i, currentValue) {
return currentValue+ "modified by fred";
});
In jQuery 1.32, the attr is defined as follow
attr: function( name, value, type ) {
var options = name;
// Look for the case where we're accessing a style value
if ( typeof name === "string" )
if ( value === undefined )
return this[0] && jQuery[ type || "attr" ]( this[0], name ); //jQuery.attr(this[0], name);
else {
options = {};
options[ name ] = value;
}
// Check to see if we're setting style values
return this.each(function(i){
// Set all the styles
for ( name in options )
jQuery.attr(
type ?
this.style :
this,
name, jQuery.prop( this, options[ name ], type, i, name )
);
});
},
But in 1.4.2, it is defined as followed.
attr: function( name, value ) {
//the access function is defined in core module
return access( this, name, value, true, jQuery.attr );
},
We can see that a protected access function really does the job.
// Mutifunctional method to get and set values to a collection
// The value/s can be optionally by executed if its a function
// elems is an array
// key, value is dictionary pair
// exec is an boolean, put it true if you want to call the value as a function
// fn is a function used to access the element
// passe is usually false, I am not sure it is intention
function access( elems, key, value, exec, fn, pass ) {
var length = elems.length;
// Setting many attributes
//if key is complext object like { name: "fred", age: 18 }
if ( typeof key === "object" ) {
for ( var k in key ) {
access( elems, k, key[k], exec, fn, value );
}
return elems;
}
// Setting one attribute
if ( value !== undefined ) {
// Optionally, function values get executed if exec is true
//if value is a function which dyanmically return a true value
//and pass is null
//and exec is true
//then set exec to true
//if caller pass is undefined and caller want to evalueate the value function and value is a function
exec = !pass && exec && jQuery.isFunction(value);
//your callback function is like
//function( elem, name, value)
//for example
//Query.fn.css = function( name, value ) {
// return access( this, name, value, true, function( elem, name, value ) {
//or function( elem, name, value, pass )
//for example attr: function( elem, name, value, pass )
for ( var i = 0; i length; i++ ) {
//fn( elems[i], key, exec ? value.call( elems[i], i, fn( elems[i], key ) ) : value, pass );
//exec means your value to set is need to be determined by the callback functio
var elem = elems[i];
var valueToSet;
if (exec)
{
//get the current value first
var currentValue = fn(elem, key);
//then call the value function to get the new value
valueToSet = value.call(elem, i , currentValue);
}
else
{
valueToSet = value;
}
fn(elem, key, valueToSet, pass);
}
return elems;
}
// Getting an attribute
return length ? fn( elems[0], key ) : undefined;
}
jQuery.fn.css method also used this protected method.
jQuery.fn.css = function( name, value ) {
//rather call function(elem, name, value) call
//access function, and let access function to call back function(elem, name, value)
return access( this, name, value, true, function( elem, name, value ) {
if ( value === undefined ) {
return jQuery.curCSS( elem, name );
}
if ( typeof value === "number" && !rexclude.test(name) ) {
value += "px";
}
jQuery.style( elem, name, value );
});
};
. In this book, it says
, author John mentions his experience in Chapter 3, "Assert, Assert, Assert, Assert". He argued with his boss about a section of code, which misused "Assert", and he said "Whoever wrote this needs to be fired! I can't believe we have an engineer on our staff who is this incredibly and completely stupid!". His boss got very quiet, grabbed the paper out of his hands, and quietly said, "That's my code." . And John resigned from the company later.
