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Initializing Props
If a property (key) doesn't exist when we try to access it with the . operator, we'll just get undefined. One way to check for this is by using the ! (not) operator because undefined is "falsy" (meaning it evaluates to false in a boolean context). The syntax is simple:
const balances = {
lane: 100,
breanna: 150,
john: 200,
};
// if bob doesn't have a balance yet
// create a new prop for him
// set to 0
if (!balances.bob) {
balances.bob = 0;
}