Promises：如何返回具有其他错误处理程序的承诺

Question

I am using tableau js api and calling worksheet.applyFilterAsync & workbook.changeParameterValueAsync methods based on certain conditions. These methods have an otherwise error handler.

I am also in between the executing flow return my custom promise like

      return new Promise((resolve, reject) => {
        resolve(true)
      });

the issue is when i am returning promise and not changeParameterValueAsync or worksheet.applyFilterAsync i am getting an error

TypeError: undefined is not a function (near '...}).otherwise(function (err) {...')

looks like the promise i return does not have a otherwise error handler?

relevant code is as follows

  const applyStep = (step) => {
    if(step.step_type == 'filter') {
      return worksheet.applyFilterAsync(step.name, values, 'replace');
    } else if(step.step_type == 'parameter') {
      return workbook.changeParameterValueAsync(`${step.name}`, value);
    } else {
      return new Promise((resolve, reject) => {
        resolve(true)
      });
    }
  };


  const applyFilters = (counter) => {
    return new Promise((resolve, reject) => {
      let filter = filters[counter];
      if(filter) {
        applyStep(filter).then(promiseTimeout(filter.delay)).then(() => resolve(applyFilters(++counter))).otherwise(function(err) {
          reject(err);
        });
      } else {
        resolve(true);
      }
    });
  };

I need the otherwise error handler to handle error returned by tableau api methods but it does not work in cases where i am returning my custom promise, may be because the promise i am returning does not have an otherwise error handler?

How can address this any help in fixing this will be really great, Thanks.

Answer 1

From the tableau docs :

otherwise(errback: Function) Promise Registers a rejection handler. Shortcut for then(null, errback).

So in your code, you could do

applyStep(filter)
.then(promiseTimeout(filter.delay))
.then(() => resolve(applyFilters(++counter)))
.then(null, function(err) {
    reject(err);
});

That is instead of .otherwise(err) you can use .then(null, err) .

Answer 2

The issue is that you are currently mixing two different types of promises. The tableau Promise and the standard JavaScript Promise . These two have different methods which currently results in issues. You can pass a tableau Promise to Promise.resolve() to convert it into a standard JavaScript Promise.

return Promise.resolve(worksheet.applyFilterAsync(step.name, values, 'replace'));

When working with the promise you now have to work with then() , catch() and finally() instead of then() , otherwise() and always() .