A JavaScript utility library delivering consistency, modularity, performance, & extras.

<script src="lodash.js"></script>

$ npm i lodash # tip: i is an alias for install

// load the modern build
var _ = require('lodash');
// or a method category
var array = require('lodash/array');
// or just a method
var chunk = require('lodash/array/chunk');

In the browser:

Using npm:

In node.js:

_.funcName(argument, iteratee);

Basic structure in use:

var arr = [1,2,3];
var sum = 0;

for (var i = 0; i < arr.length; i++) {
    sum += arr[i];
}

What you're probably doing...

var arr = [1,2,3];
var sum = arr.reduce(function (prev, curr) {
    return prev + curr;
}

What you may be doing...

var arr = [1,2,3];
var sum = _.sum(arr); // returns 6

var obj = {'a': 1, 'b': 2, 'c': 3};
var objSum = _.sum(obj); // returns 6

What you should be doing...

var matches = [];

pets.forEach(function (pet) {
	if (pet.age === 6 && pet.color === 'brown') {
		matches.push(pet);
	}
});

What you're probably doing...

var pets = [
	{name: 'Fluffy', age: 6, color: 'red'},
	{name: 'Rex', age: 6, color: 'brown'},
	{name: 'Spot', age: 6, color: 'brown'},
];

Some pets to work with...

var matches = _.where(pets, {age: 6, color: 'brown'});

What you should be doing...

for (var key in user) {
    if (user[key]) {
	user[key] = updated[key];   
    }
}

What you're probably doing...

var user = {name: 'Ryan', last: 'Dwyer', age: 25, eyes: 'brown'};
var updated = {name: 'Ryan', last: 'Dwyer', age: 26, eyes: 'blue'};

Some data to work with...

_.merge(user, updated);

What you should be doing...

function flatten(arr) {
    var flattened = [];
    for (var i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
            flattened = flattened.concat(flatten(arr[i]));
        } else {
            flattened.push(arr[i]);
        }
    }
    return flattened;
}

function square (n) {
	return n * n;
}

var flattened = flatten(arr);
flattened = flattened.map(square);
var sum = flattened.reduce(function (a, b) {
	return a + b;
});

What you're probably doing...

now with implicit chaining 

var sum = _(arr) // creates a lodash object wrapper on arr
	.flattenDeep // recursively flattens an array
	.map(n => n * n) // squares each element
	.sum(); // sums up the elements

with explicit chaining 

var sum = _.chain(arr) // creates a lodash object wrapper on arr
	.flattenDeep // recursively flattens an array
	.map(n => n * n) // squares each element
	.sum() // sums up the elements
        .value() // required to unwrap the lodash object