Arrays

Iterate

• Underscore

  _.each(array, iteratee)

• ES5.1

  array.forEach(iteratee)

Map

• Underscore

  _.map(array, iteratee)

• ES5.1

  array.map(iteratee)

Use a function to accumulate a single value from an array (left-to-right)

• Underscore

  _.reduce(array, iteratee, memo)

• ES5.1

  array.reduce(iteratee, memo)

Use a function to accumulate a single value from an array (right-to-left)

• Underscore

  _.reduceRight(array, iteratee, memo)

• ES5.1

  array.reduceRight(iteratee, memo)

Test whether all elements in an array pass a predicate

• Underscore

  _.every(array, predicate)

• ES5.1

  array.every(predicate)

Test whether some element in an array passes a predicate

• Underscore

  _.some(array, predicate)

• ES5.1

  array.some(predicate)

Find a value in an array

• Underscore

  _.find(array, predicate)

• ES2015

  array.find(predicate)

Get a property from each element in an array

• Underscore

  _.pluck(array, propertyName)

• ES2015

  array.map(value => value[propertyName])

Check if array includes an element

• Underscore

  _.includes(array, element)

• ES2016

  array.includes(element)

Convert an array-like object to array

• Underscore

  _.toArray(arguments)

• ES2015

  [...arguments]

Convert an array of keys and values to an object

• Underscore

  _.object(array)

• ES2015

  array.reduce((result, [key, val]) => Object.assign(result, {[key]: val}), {})

• Object Rest/Spread (Stage 2)

  array.reduce((result, [key, val]) => {...result, [key]: val}, {})

Create a copy of an array with all falsy values removed

• Underscore

  _.compact(array)

• ES5.1

  array.filter(Boolean)

• ES2015

  array.filter(x => !!x)

Create a copy of an array with duplicates removed

• Underscore

  _.uniq(array)

• ES2015

  [...new Set(array)]

Find the index of a value in an array

• Underscore

  _.indexOf(array, value)

• ES5.1

  array.indexOf(value)

Find the index in an array by predicate

• Underscore

  _.findIndex([4, 6, 7, 12], isPrime);

• ES2015

  [4, 6, 7, 12].findIndex(isPrime);

Create an array with n numbers, starting from x

• Underscore

  _.range(x, x + n)

• ES2015

  Array.from(Array(n), (_, i) => x + i)

Objects

Names of own enumerable properties as an array

• Underscore

  _.keys(object)

• ES5.1

  Object.keys(object)

Number of keys in an object

• Underscore

  _.size(object)

• ES5.1

  Object.keys(object).length

Names of all enumerable properties as an array

• Underscore

  _.allKeys(object)

• ES2015

  [...Reflect.enumerate(object)]

Values

• Underscore

  _.values(object)

• ES2015

  Object.keys(object).map(key => object[key])

• ES2017

  Object.values(object)

Create a new object with the given prototype and properties

• Underscore

  _.create(proto, properties)

• ES2015

  Object.assign(Object.create(proto), properties)

Create a new object from merged own properties

• Underscore

  _.assign({}, source, { a: false })

• ES2015

  Object.assign({}, source, { a: false })

• Object Rest/Spread (Stage 2)

  { ...source, a: false }

Create a shallow clone of own properties of an object

• Underscore

  _.extendOwn({}, object)

• Object Rest/Spread (Stage 2)

  { ...object }

Check if an object is an array

• Underscore

  _.isArray(object)

• ES5.1

  Array.isArray(object)

Check if an object is a finite Number

• Underscore

  _.isNumber(object) && _.isFinite(object)

• ES2015

  Number.isFinite(object)

Functions

Bind a function to an object

• Underscore

  foo(_.bind(function () {
    this.bar();
  }, this));
  
  foo(_.bind(object.fun, object));

• ES2015

  foo(() => {
    this.bar();
  });
  
  foo(() => object.fun());

Utility

Identity function

• Underscore

  _.identity

• ES2015

  value => value

A function that returns a value

• Underscore

  _.constant(value)

• ES2015

  () => value

The empty function

• Underscore

  _.noop

• ES2015

  () => {}

Get the current time in milliseconds since the epoch

• Underscore

  _.now()

• ES5.1

  Date.now()

Template

• Underscore

  var greeting = _.template("hello <%= name %>");
  greeting({ name: 'moe' });

• ES2015

  const greeting = ({ name }) => `hello ${name}`;
  greeting({ name: 'moe' });