Looping over Objects vs Arrays in Javascript (Beginner)

loops-objects-vs-arrays.js

// looping over an array
var fruit = ["Mango", "Guanabana", "Mamoncino", "Piña"];
for(var i=0; i<fruit.length; i++) {
    console.log(fruit[i]);
}

// looping over an object
var students = {
    // key : value
    // access a value with object[key]
    "raine": "A+",
    "kristina": "A-",
    "francis": "B",
    "gene": "F"
};

for(name in students) {
    console.log(name + " has a grade of " + students[name]);
}

// What if you wanted to just check the existence of a single key in the object?

// Solution A: iterate through the object, check each one: not necessary!

// when you ask for a value of a key that doesn't exist in the object, you get 
// undefined (which is actually a type in Javascript!)
students["samuel"] === undefined

// Solution B1:
if(students["samuel"] !== undefined) {
    console.log("samuel exists!");
}

// Solution B2:
if("samuel" in students) {
    console.log("samuel exists!");
}