按照承诺归还承诺

Question

我是承诺的新手，我有以下功能

var chai = require('chai');
var expect = chai.expect;

var chaiAsPromised = require('chai-as-promised');
chai.use(chaiAsPromised);

it('should do something with promises', function() {
    var blah = 'foo';

    var result = systemUnderTest();

    return expect(result).to.eventually.equal(blah);
});

为什么return之前有expect个关键字，它有什么意义？如果我们不return

会发生什么

Answer 1

您必须返回承诺以执行所有承诺链

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如果您没有退回承诺，则可以在预期评估后执行块it('should do something with promises', function() { const expected = "test"; const promise = new Promise((resolve, reject) => { ...//Something to do }); promise.then(() => { return expected; }); return expect(promise).to.eventually.equal(expected); }); ;