[英]What is wrong with my javascript for-in loop
<!DOCTYPE html>
<html>
<body>
<script language="javascript" type="text/javascript">
//Definition of staff members (class)
function StaffMember(name,discountPercent){
this.name = name;
this.discountPercent = discountPercent;
}
//Creation of staff members (object)
var s121 = new StaffMember("Sally",5);
var b122 = new StaffMember("Bob",10);
var d123 = new StaffMember("Dave",20);
staffMembers = [s121,b122,d123];
//Creation of cash register (object)
var cashRegister = {
total:0,
lastTransactionAmount: 0,
//Add to the total (method)
add: function(itemCost){
this.total += (itemCost || 0);
this.lastTransactionAmount = itemCost;
},
//Retreive the value of an item (method)
scan: function(item,quantity){
switch (item){
case "eggs": this.add(0.98 * quantity); break;
case "milk": this.add(1.23 * quantity); break;
case "magazine": this.add(4.99 * quantity); break;
case "chocolate": this.add(0.45 * quantity); break;
}
return true;
},
//Void the last item (method)
voidLastTransaction : function(){
this.total -= this.lastTransactionAmount;
this.lastTransactionAmount = 0;
},
//Apply a staff discount to the total (method)
applyStaffDiscount: function(employee) {
this.total -= this.total * (employee.discountPercent / 100);
}
};
//Ask for number of items
do {
var numOfItems = prompt("How many items do you have?");
document.body.innerHTML = numOfItems;
if (isNaN(numOfItems)) {
i=0;
} else {
i=1;
}
} while (i===0);
//Ask for item and qty of item
var items = [];
var qtys = [];
for(var i=0;i<numOfItems;i++) {
var j=0;
do {
items[i] = prompt("What are you buying? (eggs, milk, magazine, chocolate)");
switch (items[i]) {
case "eggs" :;
case "milk" :;
case "magazine" :;
case "chocolate" : j=1; document.body.innerHTML = items[i]; break;
default : document.body.innerHTML = 'Item not reconized, please re-enter...'
; break;}
} while (j===0);
do {
qtys[i] = prompt("How many " + items[i] + " are you buying?");
document.body.innerHTML = qtys[i];
if (isNaN(qtys[i])) {
j=1;
} else {
j=0;
}
} while (j===1);
//Add to the sub-total
cashRegister.scan(items[i],qtys[i])
}
//Find out if it's a staff member & if so apply a discount
var customer;
var staffNo;
do {
customer = prompt("Please enter customer name or type 'staff'.");
document.body.innerHTML = customer;
if (customer === 'staff') {
staffNo = prompt("Please enter your staff number");
for (i in staffMembers) {
if (staffMembers[i] === staffNo) {
cashRegister.applyStaffDiscount(staffNo);
} else {
document.body.innerHTML = "Staff number not found";
};
}
}
i=1;
} while (i=0);
// Show the total bill
if (customer !== 'staff') {
document.body.innerHTML = 'Your bill is £'+cashRegister.total.toFixed(2)
+' Thank you for visiting ' +customer;
} else {
document.body.innerHTML = 'Your bill is £'+cashRegister.total.toFixed(2)
+' Thank you for visiting ' +staffNo;
};
</script>
</body>
</html>
我的代碼似乎有什么問題，它的工作原理但不適用員工折扣，我覺得錯誤是存在的;
for (i in staffMembers) {
if (staffMembers[i] === staffNo) {
cashRegister.applyStaffDiscount(staffNo);
} else {
document.body.innerHTML = "Staff number not found";
};
}
任何人都可以幫助發現錯誤，我一直在學習CodeAcademy，但已經進一步檢查輸入的數據。 但我似乎無法理解為什么這部分在通過' http://www.compileonline.com/try_javascript_online.php '檢查時不能正常工作。
事實證明你的代碼存在很多問題。 要使其“正常工作”，您需要修復的關鍵事項如下：
首先 - 您要求的是“員工編號”，但您的員工結構沒有空間。 您可以按如下方式修改StaffMember ：
//Definition of staff members (class)
function StaffMember(name, number, discountPercent){
this.name = name;
this.number = number;
this.discountPercent = discountPercent;
}
//Creation of staff members (object)
var s121 = new StaffMember("Sally","s121",5);
var b122 = new StaffMember("Bob","b122",10);
var d123 = new StaffMember("Dave","d123",20);
staffMembers = [s121,b122,d123];
現在你有一個“唯一標識符” - 我決定給員工提供與變量名相同的號碼，但這不是必需的。
接下來，讓我們看一下你所擁有的循環：將其更改為
do {
customer = prompt("Please enter customer name or type 'staff'.");
document.body.innerHTML = customer;
if (customer === 'staff') {
staffNo = prompt("Please enter your staff number:");
for (i in staffMembers) {
if (staffMembers[i].number === staffNo) { // <<<<< change the comparison
cashRegister.applyStaffDiscount(staffMembers[i]); // <<<<< call applyStaffDiscount with the right parameter: the object, not the staff number
} else {
document.body.innerHTML = "Staff number not found";
};
}
}
i=1; // <<<<< I really don't understand why you have this do loop at all.
} while (i == 0); // <<<<< presumably you meant "while(i == 0)"? You had "while (i=0)"
你可以做很多很多事情來改善它 - 但至少這會讓你開始。 完整的“工作”代碼（我可能做了其他編輯，我忘了指出 - 但下面是直接從我的工作空間復制，“工作” - 雖然相當片狀）：
<!DOCTYPE html>
<html>
<body>
<script language="javascript" type="text/javascript">
//Definition of staff members (class)
function StaffMember(name, number, discountPercent){
this.name = name;
this.number = number;
this.discountPercent = discountPercent;
}
//Creation of staff members (object)
var s121 = new StaffMember("Sally","s121",5);
var b122 = new StaffMember("Bob","b122",10);
var d123 = new StaffMember("Dave","d123",20);
staffMembers = [s121,b122,d123];
//Creation of cash register (object)
var cashRegister = {
total:0,
lastTransactionAmount: 0,
//Add to the total (method)
add: function(itemCost){
this.total += (itemCost || 0);
this.lastTransactionAmount = itemCost;
},
//Retreive the value of an item (method)
scan: function(item,quantity){
switch (item){
case "eggs": this.add(0.98 * quantity); break;
case "milk": this.add(1.23 * quantity); break;
case "magazine": this.add(4.99 * quantity); break;
case "chocolate": this.add(0.45 * quantity); break;
}
return true;
},
//Void the last item (method)
voidLastTransaction : function(){
this.total -= this.lastTransactionAmount;
this.lastTransactionAmount = 0;
},
//Apply a staff discount to the total (method)
applyStaffDiscount: function(employee) {
this.total -= this.total * (employee.discountPercent / 100);
}
};
//Ask for number of items
do {
var numOfItems = prompt("How many items do you have?");
document.body.innerHTML = numOfItems;
if (isNaN(numOfItems)) {
i=0;
} else {
i=1;
}
} while (i===0);
//Ask for item and qty of item
var items = [];
var qtys = [];
for(var i=0;i<numOfItems;i++) {
var j=0;
do {
items[i] = prompt("What are you buying? (eggs, milk, magazine, chocolate)");
switch (items[i]) {
case "eggs" :;
case "milk" :;
case "magazine" :;
case "chocolate" : j=1; document.body.innerHTML = items[i]; break;
default : document.body.innerHTML = 'Item not reconized, please re-enter...'
; break;}
} while (j===0);
do {
qtys[i] = prompt("How many " + items[i] + " are you buying?");
document.body.innerHTML = qtys[i];
if (isNaN(qtys[i])) {
j=1;
} else {
j=0;
}
} while (j===1);
//Add to the sub-total
cashRegister.scan(items[i],qtys[i])
}
//Find out if it's a staff member & if so apply a discount
var customer;
var staffNo;
do {
customer = prompt("Please enter customer name or type 'staff'.");
document.body.innerHTML = customer;
if (customer === 'staff') {
staffNo = prompt("Please enter your number:");
for (i in staffMembers) {
if (staffMembers[i].number === staffNo) {
cashRegister.applyStaffDiscount(staffMembers[i]);
} else {
document.body.innerHTML = "Staff number not found";
};
}
}
i=1;
} while (i=0);
// Show the total bill
if (customer !== 'staff') {
document.body.innerHTML = 'Your bill is £'+cashRegister.total.toFixed(2)
+'<br> Thank you for visiting ' + customer;
} else {
document.body.innerHTML = 'Your bill is £'+cashRegister.total.toFixed(2)
+'<br> Thank you for visiting staff member ' +staffNo;
};
</script>
</body>
</html>
在每個單循環中，有一個來自i中的stattMembers的元素，而不是它的位置。 因此，你不會得到0,1,2但是會員[0]，工作人員[1]，工作人員[2]。 你應該考慮一下，也許一個簡單的for循環在你的情況下更好？
問題在於這些問題
if (staffMembers[i] === staffNo) {
cashRegister.applyStaffDiscount(staffNo);
}
應該是的
if (i === staffNo) {
cashRegister.applyStaffDiscount(staffMembers[i]);
}
i == staffNo應該是正確的條件。 staffMembers[i]對象就可以了。
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[英]What is the use of LeftHandSideExpression in for-in loop in JavaScript?
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