Collections

reject_.reject(list, predicate, [context]) 
Returns the values in list without the elements that the truth test (predicate) passes. The opposite of filter. predicate is transformed through iteratee to facilitate shorthand syntaxes.

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

pluck_.pluck(list, propertyName)
A convenient version of what is perhaps the most common use-case for map: extracting a list of property values.

var stooges = [{name: ‘moe’, age: 40}, {name: ‘larry’, age: 50}, {name: ‘curly’, age: 60}];
_.pluck(stooges, ‘name’);
=> [“moe”, “larry”, “curly”]

max_.max(list, [iteratee], [context]) 
Returns the maximum value in list. If an iteratee function is provided, it will be used on each value to generate the criterion by which the value is ranked. -Infinity is returned if list is empty, so an isEmpty guard may be required. Non-numerical values in list will be ignored.

var stooges = [{name: ‘moe’, age: 40}, {name: ‘larry’, age: 50}, {name: ‘curly’, age: 60}];
_.max(stooges, function(stooge){ return stooge.age; });
=> {name: ‘curly’, age: 60};

min_.min(list, [iteratee], [context]) 
Returns the minimum value in list. If an iteratee function is provided, it will be used on each value to generate the criterion by which the value is ranked. Infinity is returned if list is empty, so an isEmpty guard may be required. Non-numerical values in list will be ignored.

跟 max 相反。

shuffle_.shuffle(list) 
Returns a shuffled copy of the list, using a version of the Fisher-Yates shuffle.

_.shuffle([1, 2, 3, 4, 5, 6]);
=> [4, 1, 6, 3, 5, 2]
打乱一个数组。

sample_.sample(list, [n])
Produce a random sample from the list. Pass a number to return n random elements from the list. Otherwise a single random item will be returned.

_.sample([1, 2, 3, 4, 5, 6]);
=> 4

_.sample([1, 2, 3, 4, 5, 6], 3);
=> [1, 6, 2]
打乱并取出。

size_.size(list)
Return the number of values in the list.

_.size([1, 2, 3, 4, 5]);
=> 5

_.size({one: 1, two: 2, three: 3});
=> 3
能统计 {...} 的 ‘length’，不知道会不会用的到。

partition_.partition(list, predicate) 
Split list into two arrays: one whose elements all satisfy predicate and one whose elements all do not satisfy predicate. predicate is transformed through iteratee to facilitate shorthand syntaxes.

_.partition([0, 1, 2, 3, 4, 5], v => v%2);
=> [[1, 3, 5], [0, 2, 4]]
按条件分组

Arrays

compact_.compact(list)
Returns a copy of the list with all falsy values removed. In JavaScript, false, null, 0, “”, undefined and NaN are all falsy.

_.compact([0, 1, false, 2, ‘’, 3]);
=> [1, 2, 3]
去除所有 falsy

flatten_.flatten(array, [shallow])
Flattens a nested array (the nesting can be to any depth). If you pass shallow, the array will only be flattened a single level.

_.flatten([1, [2], [3, [[4]]]]);
=> [1, 2, 3, 4];

_.flatten([1, [2], [3, [[4]]]], true);
=> [1, 2, 3, [[4]]];
该方法在 es10 已出（flat()、flatMap()）

without_.without(array, *values)
Returns a copy of the array with all instances of the values removed.

_.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
=> [2, 3, 4]

difference_.difference(array, *others)
Similar to without, but returns the values from array that are not present in the other arrays.

_.difference([1, 2, 3, 4, 5], [5, 2, 10]);
=> [1, 3, 4]
取出该数组与后面不同的元素

union_.union(*arrays)
Computes the union of the passed-in arrays: the list of unique items, in order, that are present in one or more of the arrays.

_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2, 3, 101, 10]
虽然 es6 的 set 也支持去重，但是 union 还支持多参数。

intersection_.intersection(*arrays)
Computes the list of values that are the intersection of all the arrays. Each value in the result is present in each of the arrays.

_.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
=> [1, 2]
只取出多个数组相交(重复)的元素。

uniq_.uniq(array, [isSorted], [iteratee]) Alias: unique 
Produces a duplicate-free version of the array, using === to test object equality. In particular only the first occurrence of each value is kept. If you know in advance that the array is sorted, passing true for isSorted will run a much faster algorithm. If you want to compute unique items based on a transformation, pass an iteratee function.

_.uniq([1, 2, 1, 4, 1, 3]);
=> [1, 2, 4, 3]
好像和 union 差不多，但是多一个迭代器的选项。

zip_.zip(*arrays)
Merges together the values of each of the arrays with the values at the corresponding position. Useful when you have separate data sources that are coordinated through matching array indexes. Use with apply to pass in an array of arrays. If you’re working with a matrix of nested arrays, this can be used to transpose the matrix.

_.zip([‘moe’, ‘larry’, ‘curly’], [30, 40, 50], [true, false, false]);
=> [[“moe”, 30, true], [“larry”, 40, false], [“curly”, 50, false]]

unzip_.unzip(array) 
The opposite of zip. Given an array of arrays, returns a series of new arrays, the first of which contains all of the first elements in the input arrays, the second of which contains all of the second elements, and so on.

_.unzip([[“moe”, 30, true], [“larry”, 40, false], [“curly”, 50, false]]);
=> [[‘moe’, ‘larry’, ‘curly’], [30, 40, 50], [true, false, false]]

object_.object(list, [values]) 
Converts arrays into objects. Pass either a single list of [key, value] pairs, or a list of keys, and a list of values. Passing by pairs is the reverse of pairs. If duplicate keys exist, the last value wins.

_.object([‘moe’, ‘larry’, ‘curly’], [30, 40, 50]);
=> {moe: 30, larry: 40, curly: 50}

_.object([[‘moe’, 30], [‘larry’, 40], [‘curly’, 50]]);
=> {moe: 30, larry: 40, curly: 50}

chunk_.chunk(array, length)
Chunks an array into multiple arrays, each containing length or fewer items.

var partners = .chunk(.shuffle(kindergarten), 2);
=> [[“Tyrone”, “Elie”], [“Aidan”, “Sam”], [“Katrina”, “Billie”], [“Little Timmy”]]
按第二个参数分组。

range_.range([start], stop, [step])
A function to create flexibly-numbered lists of integers, handy for each and map loops. start, if omitted, defaults to 0; step defaults to 1. Returns a list of integers from start (inclusive) to stop (exclusive), incremented (or decremented) by step, exclusive. Note that ranges that stop before they start are considered to be zero-length instead of negative — if you’d like a negative range, use a negative step.

_.range(10);
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
_.range(1, 11);
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
_.range(0, 30, 5);
=> [0, 5, 10, 15, 20, 25]
_.range(0, -10, -1);
=> [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
_.range(0);
=> []

Functions

throttle_.throttle(function, wait, [options])
Creates and returns a new, throttled version of the passed function, that, when invoked repeatedly, will only actually call the original function at most once per every wait milliseconds. Useful for rate-limiting events that occur faster than you can keep up with.

By default, throttle will execute the function as soon as you call it for the first time, and, if you call it again any number of times during the wait period, as soon as that period is over. If you’d like to disable the leading-edge call, pass {leading: false}, and if you’d like to disable the execution on the trailing-edge, pass
{trailing: false}.

var throttled = _.throttle(updatePosition, 100);
$(window).scroll(throttled);
节流

If you need to cancel a scheduled throttle, you can call .cancel() on the throttled function.

debounce_.debounce(function, wait, [immediate])
Creates and returns a new debounced version of the passed function which will postpone its execution until after wait milliseconds have elapsed since the last time it was invoked. Useful for implementing behavior that should only happen after the input has stopped arriving. For example: rendering a preview of a Markdown comment, recalculating a layout after the window has stopped being resized, and so on.

At the end of the wait interval, the function will be called with the arguments that were passed most recently to the debounced function.

Pass true for the immediate argument to cause debounce to trigger the function on the leading instead of the trailing edge of the wait interval. Useful in circumstances like preventing accidental double-clicks on a “submit” button from firing a second time.

var lazyLayout = _.debounce(calculateLayout, 300);
$(window).resize(lazyLayout);
节流

If you need to cancel a scheduled debounce, you can call .cancel() on the debounced function.

once_.once(function)
Creates a version of the function that can only be called one time. Repeated calls to the modified function will have no effect, returning the value from the original call. Useful for initialization functions, instead of having to set a boolean flag and then check it later.

var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.

times_.times(n, iteratee, [context]) 
Invokes the given iteratee function n times. Each invocation of iteratee is called with an index argument. Produces an array of the returned values.

_.times(3, function(n){ console.log(n); });
比如说替代:
for (let i=0;i<3;i++;) {
console.log(i)
}

compose_.compose(*functions)
Returns the composition of a list of functions, where each function consumes the return value of the function that follows. In math terms, composing the functions f(), g(), and h() produces f(g(h())).

var greet = function(name){ return “hi: “ + name; };
var exclaim = function(statement){ return statement.toUpperCase() + “!”; };
var welcome = _.compose(greet, exclaim);
welcome(‘moe’);
=> ‘hi: MOE!’
把后面的函数的返回值当做参数给前面的函数。

Object

allKeys_.allKeys(object)
Retrieve all the names of object’s own and inherited properties.

function Stooge(name) {
this.name = name;
}
Stooge.prototype.silly = true;
_.allKeys(new Stooge(“Moe”));
=> [“name”, “silly”]

pairs_.pairs(object)
Convert an object into a list of [key, value] pairs. The opposite of object.

_.pairs({one: 1, two: 2, three: 3});
=> [[“one”, 1], [“two”, 2], [“three”, 3]]
把对象的键值对转换成数组。

invert_.invert(object)
Returns a copy of the object where the keys have become the values and the values the keys. For this to work, all of your object’s values should be unique and string serializable.

_.invert({Moe: “Moses”, Larry: “Louis”, Curly: “Jerome”});
=> {Moses: “Moe”, Louis: “Larry”, Jerome: “Curly”};
交换对象的键值对。

pick_.pick(object, *keys)
Return a copy of the object, filtered to only have values for the whitelisted keys (or array of valid keys). Alternatively accepts a predicate indicating which keys to pick.

_.pick({name: ‘moe’, age: 50, userid: ‘moe1’}, ‘name’, ‘age’);
=> {name: ‘moe’, age: 50}
_.pick({name: ‘moe’, age: 50, userid: ‘moe1’}, function(value, key, object) {
return _.isNumber(value);
});
=> {age: 50}

omit_.omit(object, *keys)
Return a copy of the object, filtered to omit the blacklisted keys (or array of keys). Alternatively accepts a predicate indicating which keys to omit.

_.omit({name: ‘moe’, age: 50, userid: ‘moe1’}, ‘userid’);
=> {name: ‘moe’, age: 50}
_.omit({name: ‘moe’, age: 50, userid: ‘moe1’}, function(value, key, object) {
return _.isNumber(value);
});
=> {name: ‘moe’, userid: ‘moe1’}

isEqual_.isEqual(object, other)
Performs an optimized deep comparison between the two objects, to determine if they should be considered equal.

var stooge = {name: ‘moe’, luckyNumbers: [13, 27, 34]};
var clone = {name: ‘moe’, luckyNumbers: [13, 27, 34]};
stooge == clone;
=> false
_.isEqual(stooge, clone);
=> true

isMatch_.isMatch(object, properties)
Tells you if the keys and values in properties are contained in object.

var stooge = {name: ‘moe’, age: 32};
_.isMatch(stooge, {age: 32});
=> true

isEmpty_.isEmpty(object)
Returns true if an enumerable object contains no values (no enumerable own-properties). For strings and array-like objects _.isEmpty checks if the length property is 0.

_.isEmpty([1, 2, 3]);
=> false
_.isEmpty({});
=> true

isArray_.isArray(object)
Returns true if object is an Array.

(function(){ return _.isArray(arguments); })();
=> false
_.isArray([1,2,3]);
=> true

isObject_.isObject(value)
Returns true if value is an Object. Note that JavaScript arrays and functions are objects, while (normal) strings and numbers are not.

_.isObject({});
=> true
_.isObject(1);
=> false

isNaN_.isNaN(object)
Returns true if object is NaN.
Note: this is not the same as the native isNaN function, which will also return true for many other not-number values, such as undefined.

_.isNaN(NaN);
=> true
isNaN(undefined);
=> true
_.isNaN(undefined);
=> false

isNull_.isNull(object)
Returns true if the value of object is null.

_.isNull(null);
=> true
_.isNull(undefined);
=> false

isUndefined_.isUndefined(value)
Returns true if value is undefined.

_.isUndefined(window.missingVariable);
=> true