摘要：將某個列表中的元素映射到新的列表中。判斷序列中是否存在元素滿足給定方程的條件。用來查找數組中某指定元素的索引如果找不到指定的元素則返回返回指定值在字符串對象中首次出現的位置。創建一個在經過了指定計數器之后才會被調用的方程。

Lodash 和 Underscore 是非常優秀的當代JavaScript的工具集合框架，它們被前端開發者廣泛地使用。但是，當我們現在是針對現代化瀏覽器進行開發時，很多時候我們利用的Underscore中的方法已經被ES5與ES6所支持了，如果我們希望我們的項目盡可能地減少依賴的話，我們可以根據目標瀏覽器來選擇不用Lodash或者Underscore。

Make use of native JavaScript object and array utilities before going big.  
Cody lindley, Author of jQuery Cookbook,JavaScript Enlightenment
You probably don"t need Lodash. Nice List of JavaScript methods which you can use natively.  
Daniel Lamb, Computer Scientist, Technical Reviewer of Secrets of the JavaScript Ninja, Functional Programming in JavaScript 
I guess not, but I want it.  
Tero Parviainen, Author of build-your-own-angular
I"ll admit, I"ve been guilty of overusing #lodash. Excellent resource.  
therebelrobot, Maker of web things, Facilitator for Node.js/io.js

_.each

_.map

_.every

_.some

_.reduce

_.reduceRight

_.filter

_.find

_.findIndex

_.indexOf

_.lastIndexOf

_.includes

_.keys

_.size

_.isNaN

_.reverse

_.join

_.toUpper

_.toLower

_.trim

_.repeat

_.after

遍歷一系列的元素，并且調用回調處理方程。
Iterates over a list of elements, yielding each in turn to an iteratee function.

// Underscore/Lodash
_.each([1, 2, 3], function(value, index) {
  console.log(value);
});
// output: 1 2 3

// Native
[1, 2, 3].forEach(function(value, index) {
  console.log(value);
});
// output: 1 2 3

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將某個列表中的元素映射到新的列表中。

// Underscore/Lodash
var array1 = [1, 2, 3];
var array2 = _.map(array1, function(value, index) {
  return value*2;
});
console.log(array2);
// output: [2, 4, 6]

// Native
var array1 = [1, 2, 3];
var array2 = array1.map(function(value, index) {
  return value*2;
});
console.log(array2);
// output: [2, 4, 6]

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測試數組的所有元素是否都通過了指定函數的測試。

// Underscore/Lodash
function isLargerThanTen(element, index, array) {
  return element >=10;
}
var array = [10, 20, 30];
var result = _.every(array, isLargerThanTen);
console.log(result);
// output: true

// Native
function isLargerThanTen(element, index, array) {
  return element >=10;
}

var array = [10, 20, 30];
var result = array.every(isLargerThanTen);
console.log(result);
// output: true

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判斷序列中是否存在元素滿足給定方程的條件。

// Underscore/Lodash
function isLargerThanTen(element, index, array) {
  return element >=10;
}
var array = [10, 9, 8];
var result = _.some(array, isLargerThanTen);
console.log(result);
// output: true

// Native
function isLargerThanTen(element, index, array) {
  return element >=10;
}

var array = [10, 9, 8];
var result = array.some(isLargerThanTen);
console.log(result);
// output: true

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接收一個函數作為累加器（accumulator），數組中的每個值（從左到右）開始縮減，最終為一個值。

// Underscore/Lodash
var array = [0, 1, 2, 3, 4];
var result = _.reduce(array, function (previousValue, currentValue, currentIndex, array) {
  return previousValue + currentValue;
});
console.log(result);
// output: 10

// Native
var array = [0, 1, 2, 3, 4];
var result = array.reduce(function (previousValue, currentValue, currentIndex, array) {
  return previousValue + currentValue;
});
console.log(result);
// output: 10

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接受一個函數作為累加器（accumulator），讓每個值（從右到左，亦即從尾到頭）縮減為一個值。（與 reduce() 的執行方向相反）

// Underscore/Lodash
var array = [0, 1, 2, 3, 4];
var result = _.reduceRight(array, function (previousValue, currentValue, currentIndex, array) {
  return previousValue - currentValue;
});
console.log(result);
// output: -2

// Native
var array = [0, 1, 2, 3, 4];
var result = array.reduceRight(function (previousValue, currentValue, currentIndex, array) {
  return previousValue - currentValue;
});
console.log(result);
// output: -2

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使用指定的函數測試所有元素，并創建一個包含所有通過測試的元素的新數組。

// Underscore/Lodash
function isBigEnough(value) {
  return value >= 10;
} 
var array = [12, 5, 8, 130, 44];
var filtered = _.filter(array, isBigEnough);
console.log(filtered);
// output: [12, 130, 44]

// Native
function isBigEnough(value) {
  return value >= 10;
} 
var array = [12, 5, 8, 130, 44];
var filtered = array.filter(isBigEnough);
console.log(filtered);
// output: [12, 130, 44]

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返回數組中滿足測試條件的一個元素，如果沒有滿足條件的元素，則返回 undefined。

// Underscore/Lodash
var users = [
  { "user": "barney",  "age": 36, "active": true },
  { "user": "fred",    "age": 40, "active": false },
  { "user": "pebbles", "age": 1,  "active": true }
];

_.find(users, function(o) { return o.age < 40; });
// output: object for "barney"

// Native
var users = [
  { "user": "barney",  "age": 36, "active": true },
  { "user": "fred",    "age": 40, "active": false },
  { "user": "pebbles", "age": 1,  "active": true }
];

users.find(function(o) { return o.age < 40; });
// output: object for "barney"

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用來查找數組中某指定元素的索引, 如果找不到指定的元素, 則返回 -1.

// Underscore/Lodash
var users = [
  { "user": "barney",  "age": 36, "active": true },
  { "user": "fred",    "age": 40, "active": false },
  { "user": "pebbles", "age": 1,  "active": true }
];

var index =  _.findIndex(users, function(o) { return o.age >= 40; });
console.log(index);
// output: 1

// Native
var users = [
  { "user": "barney",  "age": 36, "active": true },
  { "user": "fred",    "age": 40, "active": false },
  { "user": "pebbles", "age": 1,  "active": true }
];

var index =  users.findIndex(function(o) { return o.age >= 40; });
console.log(index);
// output: 1

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返回指定值在字符串對象中首次出現的位置。從 fromIndex 位置開始查找，如果不存在，則返回 -1。

// Underscore/Lodash
var array = [2, 9, 9];
var result = _.indexOf(array, 2);    
console.log(result); 
// output: 0

// Native
var array = [2, 9, 9];
var result = array.indexOf(2);    
console.log(result); 
// output: 0

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返回指定元素（也即有效的 JavaScript 值或變量）在數組中的最后一個的索引，如果不存在則返回 -1。從數組的后面向前查找，從 fromIndex 處開始。

// Underscore/Lodash
var array = [2, 9, 9, 4, 3, 6];
var result = _.lastIndexOf(array, 9);    
console.log(result); 
// output: 2

// Native
var array = [2, 9, 9, 4, 3, 6];
var result = array.lastIndexOf(9);    
console.log(result); 
// output: 2

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判斷元素是否在列表中

var array = [1, 2, 3];
// Underscore/Lodash - also called with _.contains
_.includes(array, 1);
// → true

// Native
var array = [1, 2, 3];
array.includes(1);
// → true

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返回某個對象所有可枚舉的鍵名。

// Underscore/Lodash 
var result = _.keys({one: 1, two: 2, three: 3});
console.log(result);
// output: ["one", "two", "three"]

// Native
var result2 = Object.keys({one: 1, two: 2, three: 3});
console.log(result2); 
// output: ["one", "two", "three"]

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返回集合大小。

// Underscore/Lodash
var result = _.size({one: 1, two: 2, three: 3});
console.log(result);
// output: 3

// Native
var result2 = Object.keys({one: 1, two: 2, three: 3}).length;
console.log(result2); 
// output: 3

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判斷是否為NaN

// Underscore/Lodash
console.log(_.isNaN(NaN));
// output: true

// Native
console.log(isNaN(NaN));
// output: true

// ES6
console.log(Number.isNaN(NaN));
// output: true

MDN:

In comparison to the global isNaN() function, Number.isNaN() doesn"t suffer the problem of forcefully converting the parameter to a number. This means it is now safe to pass values that would normally convert to NaN, but aren"t actually the same value as NaN. This also means that only values of the type number, that are also NaN, return true. Number.isNaN()

Voice from the Lodash author:

Lodash"s _.isNaN is equiv to ES6 Number.isNaN which is different than the global isNaN.  
--- jdalton

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Lodash only
將一個序列反向。

// Lodash
var array = [1, 2, 3];
console.log(_.reverse(array));
// output: [3, 2, 1]

// Native
var array = [1, 2, 3];
console.log(array.reverse());
// output: [3, 2, 1]

Voice from the Lodash author:

Lodash"s _.reverse just calls Array#reverse and enables composition like _.map(arrays, _.reverse).

It"s exposed on _ because previously, like Underscore, it was only exposed in the chaining syntax.

--- jdalton

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Lodash only
將一個序列變成一個字符串。

// Lodash
var result = _.join(["one", "two", "three"], "--");
console.log(result);
// output: "one--two--three"

// Native
var result = ["one", "two", "three"].join("--");
console.log(result)
// output: "one--two--three"

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Lodash only
將字符串大寫。

// Lodash
var result = _.toUpper("foobar");
console.log(result);
// output: "FOOBAR"

// Native
var result = "foobar".toUpperCase();
console.log(result);
// output: "FOOBAR"

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Lodash only
將字符串變為小寫。

// Lodash
var result = _.toLower("FOOBAR");
console.log(result);
// output: "foobar"

// Native
var result = "FOOBAR".toLowerCase();
console.log(result);
// output: "foobar"

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Lodash only
消去字符串起始的空白。

// Lodash
var result = _.trim(" abc ");
console.log(result);
// output: "abc"

// Native
var result = " abc ".trim();
console.log(result);
// output: "abc"

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Lodash only
重復創建字符串。

// Lodash
var result = _.repeat("abc", 2);
// output: "abcabc"

// Native
var result = "abc".repeat(2);
console.log(result);
// output: "abcabc"

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Note this is an alternative implementation
創建一個在經過了指定計數器之后才會被調用的方程。

var notes = ["profile", "settings"];
// Underscore/Lodash
var renderNotes = _.after(notes.length, render);
   notes.forEach(function(note) {
   console.log(note);
   renderNotes();
});

 // Native
notes.forEach(function(note, index) {
 console.log(note);
 if (notes.length === (index + 1)) {
   render();
 }
});

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