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No, JavaScript objects cannot have duplicate keys. The keys must all be unique.
Object. key(). It returns the values of all properties in the object as an array. You can then loop through the values array by using any of the array looping methods.
The Object. keys() method was introduced in ES6. It takes the object that you want to iterate over as an argument and returns an array containing all properties names (or keys). You can then use any of the array looping methods, such as forEach(), to iterate through the array and retrieve the value of each property.
Explanation: Object. entries() takes an object like { a: 1, b: 2, c: 3 } and turns it into an array of key-value pairs: [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ] ] . With for ... of we can loop over the entries of the so created array.
Beware of properties inherited from the object's prototype (which could happen if you're including any libraries on your page, such as older versions of Prototype). You can check for this by using the object's hasOwnProperty() method. This is generally a good idea when using for...in loops:
var user = {};
function setUsers(data) {
for (var k in data) {
if (data.hasOwnProperty(k)) {
user[k] = data[k];
}
}
}
for (var key in data) {
alert("User " + data[key] + " is #" + key); // "User john is #234"
}
Something like this:
setUsers = function (data) {
for (k in data) {
user[k] = data[k];
}
}
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