underscore (Javascript Library) Cheatsheet




Underscore is a javascript library which supports function helpers like(map, reduce, filter, pick, each...) without extending any built-in objects.

Installation

  1. Using NPM:
npm install underscore

Object functions

pick _.pick(object, keys)

const obj = {id: 1, post: "foo", userId: "bar", "created": "2019-10-19"}
_.pick(obj, userId, post, created);   // returns filtered object with selected keys
// prints { userId: "bar", post: "foo",  "created": "2019-10-19"}

extend _.extend(object, newObject)

const obj = {id: 1, post: "foo", userId: "bar", "created": "2019-10-19"}
_.extend(obj, {updated: "2019-10-19"})  // returns a object with updated key in it
// prints  {id: 1, post: "foo", userId: "bar", "created": "2019-10-19", updated: "2019-10-19"}

invert _.invert(object)

const obj = {1: id, "foo": "post", "foo": "userId"}
_.invert(obj);   // makes keys as values and values as keys
// prints {id: 1, post: "foo", userId: "bar"}

omit _.omit(object, key)

const obj = {id: 1, post: "foo", userId: "bar", "created": "2019-10-19", updated: "2019-10-19"}
_.omit(obj, updated)  // removes the specified key from the object
// prints {id: 1, post: "foo", userId: "bar", "created": "2019-10-19"}

clone _.clone(obj)

_.clone({post: "foo"}) // prints {{post: "foo}}

has _.has(obj, key)

const obj = {id: 1, post: "foo", userId: "bar", "created": "2019-10-19", updated: "2019-10-19"}
_.has(obj, userId)  // returns boolean value as per given key
// prints  true

isEmpty _.isEmpty(obj)

_.isEmpty({id:1}) // returns boolean value
//prints true

pairs _.pairs(object)

_.pairs({id: 1, post: "foo", userId: "bar"}) // converts object into an array
// prints [[id, 1],[post, "foo"],[userId, foo]]

keys _.keys(object)

_.keys({name:"foo", age: 25})
// prints [name, age]

values _.values(object)

_.values({name:"foo", age: 25})
// prints [foo, 25]

isObject(object)

_.isObject({}) //  prints true

Array Functions

first _.first(array)

const arr = [1, 2, 3, 4, 5]
_.first(arr);

indexOf _.indexOf(array, value)

const arr = [1, 2, 3, 4, 5]
_.indexOf(arr, 2)  // Returns the index of the given value present in the array or returns -1 if value is not there
// prints 1(index of the value 2 in array)

lastIndexOf _.lastIndexOf(array, 2)

const arr = [1, 2, 3, 4, 2, 5]
_.lastIndexOf(arr, 2) // Returns the index of last occurrence of the given value or returns -1 if value is not there
// prints 4

object _.object(list, values)

_.object([name, age, phone], ["foo", 25, "0000"])
//prints {name: "foo", age: 25, phone: "0000"}

range _.range(startValue, endValue)

_.range(10)   // Returns the list of integers from startValue
// prints [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
_.range(1, 11)
// prints [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
_.range([])
// prints 0

Collection Functions

each _.each(list, method)

_.each([1, 2, 3, 4], alert) // display alert for four times

map _.map(list, context)

_.map([2, 4, 6], (num) => {num*3})
// prints [6, 12, 18]

filter

_.filter([2, 3, 4, 6, 8], (num) => {num % 2 == 0})
// prints [2, 4, 6, 8]

find

_.find([4, 6, 7, 8, 11], (num) => {isPrime})
// prints 7 because it prints first occurrence that passes

reject

var odds = _.reject([1, 2, 3, 4, 5, 6], (num)=> { num % 2 == 0 })
// prints [1, 3, 5]


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