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JavaScript in Practice: Getting Started

Mistake: treating a value type as a reference type

Explore the difference between value types and reference types in JavaScript. Understand why modifying a copy of a primitive value does not affect the original, and how improper handling leads to bugs. Learn to correctly manage mutable data by encapsulating values within arrays or objects to effectively update them.

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Suppose that the increaseAge method was erroneously implemented like this:

Node.js
var people = [
    { name: 'John Hill', age: 22 },
    { name: 'Jack Chill', age: 27 }
];
function increaseAge( age ) {
    age += 1;
}
 
console.log( 'Before:', people[0].age );
increaseAge( people[0].age );
console.log( 'After:', people[0].age );

The age stays 22 even after executing the increaseAge function. ...