在 bluebird / bookshelf.js tap 函数中有什么作用

Question

bookshelf.js tap 函数有什么作用。我没有在文档中找到任何条目

  return new Library({name: 'Old Books'})
    .save(null, {transacting: t})
    .tap(function(model) {
      //code here
    }

http://bookshelfjs.org/#Bookshelf-subsection-methods

Answer 1

Bookshelf 使用 Bluebird 作为他们的承诺，我相信 .tap() 是他们特定的 Promise 方法之一。看起来它允许您在不改变通过链传递的值的情况下调用 .then()。

http://bluebirdjs.com/docs/api/tap.html

这里是 Promise#tap() 和 Promise#then() 之间区别的例子。请注意 Promise#tap() 是不是标准，并且是 Bluebird 特定的。

var Promise = require('bluebird');

function getUser() {
  return new Promise(function(resolve, reject) {
    var user = {
      _id: 12345,
      username: 'test',
      email: 'test@test.com'
    };
    resolve(user);
  });
}

getUser()
  .then(function(user) {
    // do something with `user`
    console.log('user in then #1:', user);
    // make sure we return `user` from `#then()`,
    // so it becomes available to the next promise method
    return user;
  })
  .tap(function(user) {
    console.log('user in tap:', user);
    // note that we are NOT returning `user` here,
    // because we don't need to with `#tap()`
  })
  .then(function(user) {
    // and that `user` is still available here,
    // thanks to using `#tap()`
    console.log('user in then #2:', user);
  })
  .then(function(user) {
    // note that `user` here will be `undefined`,
    // because we didn't return it from the previous `#then()`
    console.log('user in then #3:', user);
  });

Answer 2

根据 Reg“Raganwald”Braithwaite 的说法，

tap is a traditional name borrowed from various Unix shell commands. It takes a value and returns a function that always returns the value, but if you pass it a function, it executes the function for side-effects. [source]

Here 与 underscore.js 提出的问题相同。

要点是这样的：tap 所做的只是 return 它传递的对象。但是，如果它被传递一个函数，它将执行那个函数。因此，它对于调试或在现有链中执行副作用而不改变该链非常有用。

在 bluebird / bookshelf.js tap 函数中有什么作用

in bluebird / bookshelf.js what does tap function do

node.js

bookshelf.js