SAP Cloud for Customer里一个Promise的实际应用场合-阿里云开发者社区

SAP Cloud for Customer里一个Promise的实际应用场合

2021-12-02 95

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简介： There are lots of tutorials about promise in the internet.Recently I am studying the frontend code of SAP Cloud for Customer and I come across a real example of how promise is used there.Below is the Passcode logon view.

<!doctype html>
<html>
<head>
<script>
var end;
function setupDB(){
  return this.createDatabase().then(createTable).then(insertEntry).then(readEntry).then(printResult);
}
function createTable(){
  return new Promise(function(resovle, reject) {
    console.log("prepare to create table..." + Date.now());
    this._db.transaction(function(query){
      query.executeSql('create table if not exists user(id unique, user, passwd)');
    });
    setTimeout( _createTableOK.bind(this, resovle), 1000);
  });
}
function _createTableOK(resovle){
  console.log("table created successfully..." + Date.now());
  resovle();
}
function createDatabase(){
  return new Promise(function(resovle, reject) {
    console.log("prepare to create database..." + Date.now());
    this._db = openDatabase('mydb','1.0', 'JerryTestdb',1024);
    setTimeout( _createDatabaseOK.bind(this, resovle), 1000);
  });
}
function _createDatabaseOK(resovle){
  console.log("database created successfully..." + Date.now());
  resovle(this._db);
}
function insertEntry(){
  return new Promise(function(resolve, reject) {
    this._db.transaction(function(query){
      query.executeSql("insert into user values (1,'Jerry','1234')");
    });
    setTimeout( _insertEntryOK.bind(this, resolve), 1000);
  });
}
function _insertEntryOK(resolve){
  console.log("entry inserted to table successfully..." + Date.now()); 
  resolve();
}
function readEntry() {
  return new Promise(function(resolve, reject) {
      this._db.transaction( function(query) {
        query.executeSql('select * from user',[],function(u,results) {
        setTimeout( _readEntryOK.bind(this, resolve, results), 1000);
      }); // end of query.executeSql
   } // end of function(query)
   ); // end of this._db.transaction
 });
}
function _readEntryOK(resolve, oResult){
  console.log("entry readed from DB successfully..." + Date.now());
  resolve(oResult);
}
function printResult(oResults){
  for( var i = 0; i < oResults.rows.length; i++) {
      document.writeln('id: ' + oResults.rows[i].id);
      document.writeln('user: ' + oResults.rows[i].user);
      document.writeln('passwd: ' + oResults.rows[i].passwd);
  }
  end = true;
}
function work(){
  if( end ){
    clearInterval(handle);
  }
  else{
    console.log(" working..." + Date.now());
  }
}
setupDB();
var handle = setInterval( work, 200);
</script>
</head>
</html>

SAP Cloud for Customer里一个Promise的实际应用场合

汪子熙

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