JS: Problems with for…in
JavaScript for...in iterates enumberable properties of an object.
for...in can be used in object and array
// book object
var booksObj = {
b1: "normal book",
b2: "great book",
b3: "awesome book"
};
// book array
var booksArray = ["normal book", "great book", "awesome book"]
var bookHubObj = "";
var bookHubArray = "";
for (var key in booksObj) {
bookHubObj += booksObj[key] + "\n";
}
for (var key in booksArray) {
bookHubArray += booksArray[key] + "\n";
}
// output: normal book, great book, awesome book
console.log(bookHubObj);
console.log(bookHubArray);
Problem: for...in iterates over an object prototype properties if those properties are enumberable.
Object.prototype.cat = "Tiramisu";
var dogs = {
dog1: "Tico",
dog2: "Luna",
dog3: "Toby"
}
var dogHub = [];
for (var key in dogs) {
dogHub.push(dogs[key]);
}
// output: ["Tico", "Luna", "Toby", "Tiramisu"]
console.log(dogHub);
Solution: hasOwnProperty
Object.prototype.cat = "Tiramisu";
var dogs = {
dog1: "Tico",
dog2: "Luna",
dog3: "Toby"
}
var dogHub = [];
for (var key in dogs) {
if (dogs.hasOwnProperty(key)) {
dogHub.push(dogs[key]);
}
}
// output: ["Tico", "Luna", "Toby"]
console.log(dogHub);