JS Array Methods Example

Documentation:

What I've Learned

JavaScript map, filter, find, and findIndex methods are super handy for developers because we're constantly dealing with data. Getting to know more about these methods allow you to extract, find and restructure the arrays. These four methods all accept the same three parameters element,index,array.

Map()

It's like a loop function, iterates over elements in an array.
Can reformat or transform elements in an array into a new structure
Creates a new set of data from an existing array without modifying the original array.
Useful for chaining with other methods, such as filter(), as both return new arrays.

The fruitLengths function iterates over each element in the fruits array and finds the length of each fruit.

Example:

const fruits = ['strawberry', 'grape', 'raspberry', 'watermelon', 'kiwi', 'lemon', 'blueberry', 'orange', 'grapefruit', 'banana'];

const fruitLengths = fruits.map(fruit => fruit.length)

console.log(lengthOfFruits);
// Output: [ 10, 5, 9, 10, 4, 5, 9, 6, 10, 6]

Base on the fruits array, it contains the names of the fruits. To restucture the fruits array, we can also return it into an array of object.

Example:

const selectFruit = (fruits) => {
    return fruits.map((fruit, index) => ({ fruit, index }));
}

//Output
//   { fruit: 'strawberry', index: 0 },
//   { fruit: 'grape', index: 1 },
//   { fruit: 'raspberry', index: 2 },
//   { fruit: 'watermelon', index: 3 },
//   { fruit: 'kiwi', index: 4 },
//   { fruit: 'lemon', index: 5 },
//   { fruit: 'blueberry', index: 6 },
//   { fruit: 'orange', index: 7 },
//   { fruit: 'grapefruit', index: 8 },
//   { fruit: 'banana', index: 9 }

By placing curly braces {} around the key-value pairs inside the parentheses (), you are using what’s known as an object literal. The fruit and index are used as keys and values inside the new object.

find()

Starts with the first element in the array and checks if it matches a condition. If not, it continues to the next element until a match is found or the end of the array is reached.
If a matching element is found, it returns that element. If not, it returns undefined.
This method is useful when you want to find a specific element in an array.

findPenByBrand function is to find a specific element in the inventory array where the brand is "kaweco".

Example:

const inventory = [
    {brand: "lamy", quantity: 10},
    {brand: "kaweco", quantity: 18},
    {brand: "platinum", quantity: 9},
    {brand: "pilot", quantity: 20},
    {brand: "sailor", quantity: 15},
];

const findPenByBrand = inventory.find((fountainPen) => fountainPen.brand === "kaweco")

console.log(findPenByBrand);
//Output { brand: 'kaweco', quantity: 18 }

findIndex()

This method behaves similarly to find(), checking each element in an array until it finds one that matches a given condition.
The difference is that it returns the index of the element instead of the element itself.
This method is useful when you want to find the index of a specific element in an array.

Example:

const getIndexOfBrand = inventory.findIndex((item) => item.brand === 'sailor');

console.log(`Index:`,getIndexOfBrand(inventory));
//Output Index: 4

filter()

Extracts the specific element from the array that you're looking for

The getLowStockBrands function filters items from the inventory that have a quantity less than or equal to 18. It then chains with map() to return only the brand names of the matching items, using map() as an example of how chaining methods work.

Example:

const inventory = [
    {brand: "kaweco", quantity: 18},
    {brand: "lamy", quantity: 33},
    {brand: "platinum", quantity: 22},
    {brand: "pilot", quantity: 20},
    {brand: "sailor", quantity: 18},
    {brand: "twisbi", quantity: 26},
];

const getLowStockBrands = inventory.filter(item => item.quantity <= 18).map(item => item.brand);

console.log(`Low in stock:`,getLowStockBrands);
//Output Low in stock: [ 'kaweco', 'sailor' ]

countLowStockBrands function extracts the total items that have a quantity of 18 in the inventory. The .length property then counts how many items are in that array.

Example:

const countLowStockBrands = inventory.filter(item => item.quantity === 18).length;

console.log(`Low in stock:`,countLowStockBrands); // Output Low in stock: 2

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