Objects with named properties

The idea

An object groups related values under property names. In { title: "Read", done: false }, title and done are keys, and the text and boolean are their values. Curly braces create the object; a colon connects a key to a value; commas separate properties. Dot notation such as task.title reads a known property.

A property can be updated with assignment: task.done = true. This edits the existing object. A function can receive an object in a parameter and read its fields just as it reads any other input. Returning a label does not require creating a class or using inheritance. Object literals are enough for small records and are useful preparation for TypeScript object types.

A missing property normally reads as undefined. State which properties your function requires and start with objects that have that shape. Later chapters teach copying, methods, classes, and validating data from outside your program; here, concentrate on a named record and a clear returned value.

const task = { title: "Read", minutes: 10 };
function describe(item) {
  return item.title + ": " + item.minutes;
}
task.minutes = 15;
console.log(describe(task));
console.log(task.title);

Read: 15
Read

The function reads two properties. Changing minutes updates the number while preserving the title.