Lodash 源码分析

# mapToArray

# Description

将 Map 结构转换成 [[key, value]] 的数组

# Params

{Object} map

# Return

Array

# Code

function mapToArray(map) {
  let index = -1
  const result = new Array(map.size)

  map.forEach((value, key) => {
    result[++index] = [key, value]
  })
  return result
}

# Analyze

  1. 根据 map.size 初始化数组的长度
  2. map.forEach 遍历，往数组对应的下标中添加对应的 key value 数组

# Remark

  1. Map.prototype.forEach() MDN (opens new window) 方法按照插入顺序依次对 Map 中每个键 / 值对执行一次给定的函数
  2. 另一种实现思路
function mapToArray(map) {
  const result = []
  const entries = map.entries()
  while (1) {
    const {value, done} = entries.next()
    if (done) break
    result.push(value)
  }
  return result
}
  1. Map.prototype.entries() MDN (opens new window) 方法返回一个新的包含 [key, value] 对的 Iterator 对象，返回的迭代器的迭代顺序与 Map 对象的插入顺序相同。

# Example

const map = new Map

for (let i = 0; i < 5; i++) {
  map.set('key'+i, 'value'+i)
}

/**
 *
 * [
 *  [ 'key0', 'value0' ],
 *  [ 'key1', 'value1' ],
 *  [ 'key2', 'value2' ],
 *  [ 'key3', 'value3' ],
 *  [ 'key4', 'value4' ]
 * ]
 *
 * */
console.log(mapToArray(map))

function mapToArraySelf(map) {
  const result = []
  const entries = map.entries()
  while (1) {
    const {value, done} = entries.next()
    if (done) break
    result.push(value)
  }
  return result
}

/**
 *
 * [
 *  [ 'key0', 'value0' ],
 *  [ 'key1', 'value1' ],
 *  [ 'key2', 'value2' ],
 *  [ 'key3', 'value3' ],
 *  [ 'key4', 'value4' ]
 * ]
 *
 * */

console.log(mapToArraySelf(map))

← matchesStrictComparable →