JavaScript - example of data structure mutation

javascript-mutation.js

/**--------------------- ARRAY ---------------------*/
const species = ['octopus', 'squid', 'shark',];

console.log('initial state', species);
// outputs: 'octopus', 'squid', 'shark'

// 'push' method mutates the array
// by adding a new item to its set
species.push('seahorse');

console.log('mutated state', species);
// outputs: 'octopus', 'squid', 'shark', 'seahorse'

/**--------------------- OBJECT ---------------------*/
const person = { name: 'John Doe', };

console.log('initial state', person.name);
// outputs: 'John Doe'

// overwrites the initial property value
person.name = 'Janie Doe';

console.log('mutated state', person.name);
// outputs: 'Janie Doe'