Accessing Properties

The most direct way to access a property is by name: object.foo. An alternative is to write object["foo"]. These are equivalent, but the form object.foo is more efficient. That's because when you use the object["foo"] the JavaScript may need to convert the string to an internal XS identifier at runtime.

If the value between braces ([]) is a constant that is a valid JavaScript property name, use the direct form.

The most common use of the object["foo"] form is in with a for-in loop. In this case the code using the [] notation doesn't know the name of the property, so it cannot use the more direct object.foo form. Another reason is because a property name cannot be expressed using the direct form, for example because it is a number or contains a space.

for (let name in obj) {
	const value = obj[name];
	trace(`${name} = ${value}\n`);
}

let v1 = obj[12];
let v2 = obj["a property"];

Note: Often when code uses [] notation to access properties, it is a sign that a Map may be a better choice.