其工作就是给元素创建一个属性，这个属性是一个对象，然后把与这个元素相关的信息放到这个对象里面，缓存起来。这样需要使用到这个对象的信息时，只要知道这个对象就可以拿到：
function Data() { this.expando = jQuery.expando + Data.uid++; } Data.uid = 1; //删除部分没用到代码 Data.prototype = { cache: function( owner ) { // 取出缓存，可见缓存就是目标对象的一个属性 var value = owner[ this.expando ]; // 如果对象还没有缓存，则创建一个 if ( !value ) { value = {}; // We can accept data for non-element nodes in modern browsers, // but we should not, see #8335. // Always return an empty object. if ( acceptData( owner ) ) { // If it is a node unlikely to be stringify-ed or looped over // use plain assignment if ( owner.nodeType ) { owner[ this.expando ] = value; // Otherwise secure it in a non-enumerable property // configurable must be true to allow the property to be // deleted when data is removed } else { Object.defineProperty( owner, this.expando, { value: value, configurable: true } ); } } } return value; }, get: function( owner, key ) { return key === undefined ? this.cache( owner ) : // Always use camelCase key (gh-2257) 驼峰命名 owner[ this.expando ] && owner[ this.expando ][ jQuery.camelCase( key ) ]; }, remove: function( owner, key ) { var i, cache = owner[ this.expando ]; if ( cache === undefined ) { return; } if ( key !== undefined ) { // Support array or space separated string of keys if ( jQuery.isArray( key ) ) { // If key is an array of keys... // We always set camelCase keys, so remove that. key = key.map( jQuery.camelCase ); } else { key = jQuery.camelCase( key ); // If a key with the spaces exists, use it. // Otherwise, create an array by matching non-whitespace key = key in cache ? [ key ] : ( key.match( rnotwhite ) || [] ); } i = key.length; while ( i-- ) { delete cache[ key[ i ] ]; } } // Remove the expando if there's no more data if ( key === undefined || jQuery.isEmptyObject( cache ) ) { // Support: Chrome <=35 - 45 // Webkit & Blink performance suffers when deleting properties // from DOM nodes, so set to undefined instead // https://bugs.chromium.org/p/chromium/issues/detail?id=378607 (bug restricted) if ( owner.nodeType ) { owner[ this.expando ] = undefined; } else { delete owner[ this.expando ]; } } }, hasData: function( owner ) { var cache = owner[ this.expando ]; return cache !== undefined && !jQuery.isEmptyObject( cache ); } };