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let obj = {
key1: "value1",
key2: "value2"
};
// method 1
obj.key3 = "value3";
// method 2
obj["key4"] = "value4";
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var element = {}, cart = [];
element.id = id;
element.quantity = quantity;
cart.push(element);
// Array of Objects in form {element: {id: 10, quantity: 10} }
var element = {}, cart = [];
element.id = id;
element.quantity = quantity;
cart.push({element: element});