Pure functions and higher-order functions

pure function

• As long as it is the same input (actual parameter), the same output (return) must be obtained
• Do not overwrite parameter data
• Does not produce any side effects such as network requests, input and output devices
• Cannot call Data.now()or Math.random()wait for impure methods
• Redux reducerfunctions must be pure functions

higher order functions

• 参数是函数or 返回是参数a function of
• Common high-order functions: timer setting functions, arrays forEach()/map()/filter()/find()/bind(), Promise, etc.