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JavaScript in Practice: Getting Started

Mistake: treating a value type as a reference type

Learn about the common mistake of treating a value type as a reference type.

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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. ...