jQuery源码分析16: .hide()与.show()
hide: function( speed, easing, callback ) {
if ( speed || speed === 0 ) { //< 当提供speed参数时使用animate动画隐藏DOM结点
return this.animate( genFx("hide", 3), speed, easing, callback);
} else { //< 当不提供任何参数时,先遍历jQuery对象,缓存每一个DOM结点的display值以便调用.show()时恢复原先的display值,然后将display值设置为none
var elem, display,
i = 0,
j = this.length;
for ( ; i < j; i++ ) {
elem = this[i];
if ( elem.style ) {
display = jQuery.css( elem, "display" );
if ( display !== "none" && !jQuery._data( elem, "olddisplay" ) ) {
jQuery._data( elem, "olddisplay", display );
}
}
}
// Set the display of the elements in a second loop
// to avoid the constant reflow
for ( i = 0; i < j; i++ ) {
if ( this[i].style ) {
this[i].style.display = "none";
}
}
return this;
}
},
//< .show()原理与.hide()相似,.hide()中使用.data()缓存的值用于这里调用.show()里恢复
show: function( speed, easing, callback ) {
var elem, display;
if ( speed || speed === 0 ) {
return this.animate( genFx("show", 3), speed, easing, callback );
} else {
for ( var i = 0, j = this.length; i < j; i++ ) {
elem = this[ i ];
if ( elem.style ) {
display = elem.style.display;
// Reset the inline display of this element to learn if it is
// being hidden by cascaded rules or not
if ( !jQuery._data(elem, "olddisplay") && display === "none" ) {
display = elem.style.display = "";
}
// Set elements which have been overridden with display: none
// in a stylesheet to whatever the default browser style is
// for such an element
if ( display === "" && jQuery.css(elem, "display") === "none" ) {
jQuery._data( elem, "olddisplay", defaultDisplay(elem.nodeName) );
}
}
}
// Set the display of most of the elements in a second loop
// to avoid the constant reflow
for ( i = 0; i < j; i++ ) {
elem = this[ i ];
if ( elem.style ) {
display = elem.style.display;
if ( display === "" || display === "none" ) {
elem.style.display = jQuery._data( elem, "olddisplay" ) || "";
}
}
}
return this;
}
},
其中defaultDisplay函数定义目的为获取不同元素默认的display值.
var elemdisplay = {};
// Try to restore the default display value of an element
//< 获取不同元素默认的display值,缓存在elemdisplay中
function defaultDisplay( nodeName ) {
if ( !elemdisplay[ nodeName ] ) {
var body = document.body,
elem = jQuery( "<" + nodeName + ">" ).appendTo( body ),
display = elem.css( "display" );
elem.remove();
// If the simple way fails,
// get element's real default display by attaching it to a temp iframe
if ( display === "none" || display === "" ) {
// No iframe to use yet, so create it
if ( !iframe ) {
iframe = document.createElement( "iframe" );
iframe.frameBorder = iframe.width = iframe.height = 0;
}
body.appendChild( iframe );
// Create a cacheable copy of the iframe document on first call.
// IE and Opera will allow us to reuse the iframeDoc without re-writing the fake HTML
// document to it; WebKit & Firefox won't allow reusing the iframe document.
if ( !iframeDoc || !iframe.createElement ) {
iframeDoc = ( iframe.contentWindow || iframe.contentDocument ).document;
iframeDoc.write( ( document.compatMode === "CSS1Compat" ? "<!doctype html>" : "" ) + "<html><body>" );
iframeDoc.close();
}
elem = iframeDoc.createElement( nodeName );
iframeDoc.body.appendChild( elem );
display = jQuery.css( elem, "display" );
body.removeChild( iframe );
}
// Store the correct default display
elemdisplay[ nodeName ] = display;
}
return elemdisplay[ nodeName ];
}