Pramise

function getData( url ) {
    return new Promise( ( resolve, reject ) => {
        $.get( {
            url: url,
            success: function ( data ) {
                resolve( data )
            }
        } )
    } )
}
getData( "http://jsonplaceholder.typicode.com/posts?userId=2" ).then( () => {
    console.log( 111 )
    return getData( "http://jsonplaceholder.typicode.com/posts?userId=1" )
} ).then( ( data ) => {
    console.log( 222 )
    console.log( data )
} )

promise 對象異步操作成功之后，將then方法的函數(shù)傳入作為resolve回調(diào)函數(shù)調(diào)用，第一個(gè)then方法作為回調(diào)函數(shù)調(diào)用之后又返回了一個(gè)promise對象，既可以鏈?zhǔn)秸{(diào)用then方法