javascript - promise : how to pass function with parameters?

Question

在下面的测试代码中，我尝试将带有参数(即 t2、t3)的预定义函数传递给 then。但它提示“r”未定义。

var Promise = require('bluebird');

var t2 = function(r) {
    console.log("2r: " + r);
    return 2 * r;
};

var t3 = function(r) {
    console.log("3r: " + r);
    return 3 * r;
};

new Promise(function(resolve, reject) {

    setTimeout(function() {
        resolve(1);
        reject(2)
    }, 1000);
})
.then(t2(r), t3(r))
.then(t2(r), t3(r))
.then(t2(r), t3(r));

Answer 1

只需传递函数名称即可:

var t2 = function(r) {
  console.log("2r: " + r);
  return 2 * r;
};

var t3 = function(r) {
  console.log("3r: " + r);
  return 3 * r;
};

new Promise(function(resolve, reject) {

    setTimeout(function() {
      resolve(1);
      reject(2)
    }, 1000); // (*)

  })
  .then(t2, t3)
  .then(t2, t3)
  .then(t2, t3);

如果您实际上想传递您事先知道的其他参数，请使用t2和t3>高阶函数返回函数，以便您可以在.then的参数列表中调用:

var t2 = extra => r => {
  console.log("2r: " + r);
  console.log('extra param: ' + extra);
  return 2 * r;
};

var t3 = extra => r => {
  console.log("3r: " + r);
  console.log('extra param: ' + extra);
  return 3 * r;
};


const r = 'foo';
new Promise(function(resolve, reject) {

    setTimeout(function() {
      resolve(1);
      reject(2)
    }, 1000); // (*)

  })
  .then(t2(r), t3(r))
  .then(t2(r), t3(r))
  .then(t2(r), t3(r));