计算器功能的JavaScript承诺

Question

Been trying to figure out this coding challenge and I've hit a wall. It's either way over my head or I'm just missing something obvious. Below is the code I've got so far as well as the mocha test I'm trying to create the function to satisfy.

// Setup Mocha and Chai

mocha.setup( "bdd" );
var expect = chai.expect;

class Calculator {

  add(x, y) {
    return x + y;
  }

  subtract(x, y) {
    return x - y;
  }

  multiply(x, y) {
    return x * y;
  }

  divide(x, y) {
    if(y === 0) {
      return NaN;
    } else {
      return x / y
    }
  }

  calculate(...args) {
    var result = 0;
    return new Promise(function(resolve, reject){
      setTimeout(function() {
       if(result === NaN) {
         reject();
       } else {
         resolve();
       }
      }, 1000);
    });
  }
}

/** * 4. Add a calculate function to Calculator that matches this specification */

describe( "Calculator.calculate", function(){
  var calculator;

  beforeEach( function(){
    calculator = new Calculator();
  } );

  it( "returns a promise", function(){
    var calculating = calculator.calculate( function(){} );
    expect( calculating ).to.be.instanceOf( Promise );
  } );

  it( "resolves when the calculation succeeds", function( done ){
    var calculating = calculator.calculate( function(){
      expect( this ).to.equal( calculator );
      var result = 0;
      result += this.add( 1, 2 );
      result += this.add( 3, 4 );
      return result;
    } );
    calculating.then( function( result ){
      expect( result ).to.equal( 10 );
      done();
    } );
  } );

  it( "rejects when the calculation fails", function( done ){
    var calculating = calculator.calculate();
    calculating.catch( function( result ){
      expect( result ).to.be.NaN;
      done();
    } );
  } );
} );

// Run the tests

mocha.run();

The Calculator class was for a different test. I'm having trouble with the calculate function and getting it to pass the test here at the bottom. Any thought or insights?

** This is the error I get -- Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. https://cdnjs.cloudflare.com/ajax/libs/mocha/4.0.1/mocha.min.js:1:38622

Thanks!

Answer 1

Your code is a bit messy, but I give you an example, using your code, on how to do a promise for a calculator function.

The promise function must always wrap the asynchronous function around. Then you call resolve or reject accordingly, whether there is an error.

 /* First define the calculator with the promise*/ function calculateDivision(x,y, time) { var result = 0; return new Promise(function(resolve, reject){ setTimeout(function() { result = x/y; if(!isFinite(result)) { reject(result); } else { resolve(result); } }, time); }); } /*now define the calculator using promise*/ function divide(x,y, time){ calculateDivision(x,y, time).then(function(result){ console.log("success:" + result); }, function(reason){ console.log("error: " + reason); }); } /*results will come inverted cause of time to calculate*/ divide(9,3, 2000); //divide 9 by 3 after 2 seconds divide(1,0, 1000); //divide 1 by 0 after 1 second divide(1000, 2, 500); //divide 1000 by 2 after 500 miliseconds 

Run this script and you'll see