Lodash 常见的方程用法

Lodash Common function Collection

1. reduce

.reduce(collection, [iteratee=.identity], [accumulator])

Reduces collection to a value which is the accumulated result of running each element in collection thru iteratee, where each successive invocation is supplied the return value of the previous. If accumulator is not given, the first element of collection is used as the initial value. The iteratee is invoked with four arguments:
(accumulator, value, index|key, collection).

return

Returns the accumulated value.

_.reduce([1, 2], function(sum, n) {
  return sum + n;
}, 0);
// => 3
 
_.reduce({ 'a': 1, 'b': 2, 'c': 1 }, function(result, value, key) {
  (result[value] || (result[value] = [])).push(key);
  return result;
}, {});
// => { '1': ['a', 'c'], '2': ['b'] } (iteration order is not guaranteed)

2. map

.map(collection, [iteratee=.identity])

Creates an array of values by running each element in collection thru iteratee. The iteratee is invoked with three arguments:
(value, index|key, collection).

return

Returns the new mapped array.

function square(n) {
  return n * n;
}
 
_.map([4, 8], square);
// => [16, 64]
 
_.map({ 'a': 4, 'b': 8 }, square);
// => [16, 64] (iteration order is not guaranteed)
 
var users = [
  { 'user': 'barney' },
  { 'user': 'fred' }
];
 
// The `_.property` iteratee shorthand.
_.map(users, 'user');
// => ['barney', 'fred']

3. forEach (iterate over an array)

.forEach(collection, [iteratee=.identity])

Iterates over elements of collection and invokes iteratee for each element. The iteratee is invoked with three arguments: (value, index|key, collection). Iteratee functions may exit iteration early by explicitly returning false.

return

Returns original collection.

_.forEach([1, 2], function(value) {
  console.log(value);
});
// => Logs `1` then `2`.
 
_.forEach({ 'a': 1, 'b': 2 }, function(value, key) {
  console.log(key);
});
// => Logs 'a' then 'b' (iteration order is not guaranteed).

4. forIn

.forIn(object, [iteratee=.identity])

Iterates over own and inherited enumerable string keyed properties of an object and invokes iteratee for each property. The iteratee is invoked with three arguments: (value, key, object). Iteratee functions may exit iteration early by explicitly returning false.

return

Returns original object.

function Foo() {
  this.a = 1;
  this.b = 2;
}
 
Foo.prototype.c = 3;
 
_.forIn(new Foo, function(value, key) {
  console.log(key);
});
// => Logs 'a', 'b', then 'c' (iteration order is not guaranteed).

4. deepClone

_.cloneDeep(value)

This method is like _.clone except that it recursively clones value.

return

Returns the deep cloned value.

var objects = [{ 'a': 1 }, { 'b': 2 }];
 
var deep = _.cloneDeep(objects);
console.log(deep[0] === objects[0]);
// => false

5. find

.find(collection, [predicate=.identity], [fromIndex=0])

Iterates over elements of collection, returning the first element predicate returns truthy for. The predicate is invoked with three arguments: (value, index|key, collection).

returns

Returns the matched element, else undefined.

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; });
// => object for 'barney'
 
// The `_.matches` iteratee shorthand.
_.find(users, { 'age': 1, 'active': true });
// => object for 'pebbles'
 
// The `_.matchesProperty` iteratee shorthand.
_.find(users, ['active', false]);
// => object for 'fred'
 
// The `_.property` iteratee shorthand.
_.find(users, 'active');
// => object for 'barney'