TypeError：無法讀取未定義的屬性“toNumber”

無法讀取未定義的屬性“toNumber”？

錯誤資訊

1. 合約：DappTokenSale 結束代幣銷售：TypeError:Cannot read property ’toNumber’ of undefined at test/DappTokenSale.js:85:28 at process.internalTickCallback (internal/process/next_tick.js:77:7)

程式碼

var DappToken = artifacts.require('./DappToken.sol');
var DappTokenSale = artifacts.require('./DappTokenSale.sol');

contract('DappTokenSale', function(accounts) {
var tokenInstance;
var tokenSaleInstance;
var admin = accounts[0];
var buyer = accounts[1];
var tokenPrice = 1000000000000000; // in wei
var tokensAvailable = 750000;
var numberOfTokens;

it('initializes the contract with the correct values', function() {
return DappTokenSale.deployed().then(function(instance) {
 tokenSaleInstance = instance;
 return tokenSaleInstance.address
}).then(function(address) {
 assert.notEqual(address, 0x0, 'has contract address');
 return tokenSaleInstance.tokenContract();
}).then(function(address) {
 assert.notEqual(address, 0x0, 'has token contract address');
 return tokenSaleInstance.tokenPrice();
}).then(function(price) {
 assert.equal(price, tokenPrice, 'token price is correct');
});
});

it('facilitates token buying', function() {
return DappToken.deployed().then(function(instance) {
 // Grab token instance first
 tokenInstance = instance;
 return DappTokenSale.deployed();
}).then(function(instance) {
 // Then grab token sale instance
 tokenSaleInstance = instance;
 // Provision 75% of all tokens to the token sale
 return tokenInstance.transfer(tokenSaleInstance.address, tokensAvailable, { from: admin })
}).then(function(receipt) {
 numberOfTokens = 10;
 return tokenSaleInstance.buyTokens(numberOfTokens, { from: buyer, value: numberOfTokens * tokenPrice })
}).then(function(receipt) {
 assert.equal(receipt.logs.length, 1, 'triggers one event');
 assert.equal(receipt.logs[0].event, 'Sell', 'should be the "Sell" event');
 assert.equal(receipt.logs[0].args._buyer, buyer, 'logs the account that purchased the tokens');
 assert.equal(receipt.logs[0].args._amount, numberOfTokens, 'logs the number of tokens purchased');
 return tokenSaleInstance.tokensSold();
}).then(function(amount) {
 assert.equal(amount.toNumber(), numberOfTokens, 'increments the number of tokens sold');
 return tokenInstance.balanceOf(buyer);
}).then(function(balance) {
 assert.equal(balance.toNumber(), numberOfTokens);
 return tokenInstance.balanceOf(tokenSaleInstance.address);
}).then(function(balance) {
 assert.equal(balance.toNumber(), tokensAvailable - numberOfTokens);
 // Try to buy tokens different from the ether value
 return tokenSaleInstance.buyTokens(numberOfTokens, { from: buyer, value: 1 });
}).then(assert.fail).catch(function(error) {
 assert(error.message.indexOf('revert') >= 0, 'msg.value must equal number of tokens in wei');
 return tokenSaleInstance.buyTokens(800000, { from: buyer, value: numberOfTokens * tokenPrice })
}).then(assert.fail).catch(function(error) {
 assert(error.message.indexOf('revert') >= 0, 'cannot purchase more tokens than available');
});
});

it('ends token sale', function() {
return DappToken.deployed().then(function(instance) {
 // Grab token instance first
 tokenInstance = instance;
 return DappTokenSale.deployed();
}).then(function(instance) {
 // Then grab token sale instance
 tokenSaleInstance = instance;
 // Try to end sale from account other than the admin
 return tokenSaleInstance.endSale({ from: buyer });
}).then(assert.fail).catch(function(error) {
 assert(error.message.indexOf('revert' >= 0, 'must be admin to end sale'));
 // End sale as admin
 return tokenSaleInstance.endSale({ from: admin });
}).then(function(receipt) {
 return tokenInstance.balanceOf(admin);
}).then(function(balance) {
 assert.equal(balance.toNumber(), 999990, 'returns all unsold dapp tokens to admin');
 // Check that the contract has no balance
 }).then(function(price) {
   assert.equal(price.toNumber(), 0, 'token price was reset');
});
});
});

問題似乎在這裡：

.then(function(balance) {
  assert.equal(balance.toNumber(), 999990, 'returns all unsold dapp tokens to admin');
  // Check that the contract has no balance
}).then(function(price) {
  assert.equal(price.toNumber(), 0, 'token price was reset');
});

第一個函式沒有返回值，所以當然price是未定義的。

.then((balance) => {
       assert.equal(
         balance.toNumber(),
         999990,
         "balance left with admin after ending sale"
       );
       return tokenInstance.balanceOf(tokenSaleInstance.address);
     })
     .then((balance) => {
       assert.equal(balance.toNumber(), 0, "contract has been reset");
     });

引用自：https://ethereum.stackexchange.com/questions/65464