Functional Programming

• a paradigm, a style of building the structure and elements of computer programs
• to understand functional programming we should understand pure functions.

pure functions

• It returns the same result if given the same arguments.
• it does not cause any side effect.
• if it’s not pure then it’s using a variable was not passed as a parameter.
• so pure functions do calculations and return value** result of passed parameter**.
• when it also read an external file it’s not pure.
• Any function that relies on a random number generator cannot be pure, because it rely on global variable.
• if modify global variable it’s not pure function.
• Pure functions are stable, consistent, and predictable.

Pure functions benefits

• easier to test.
• easier to deal with it.
• it does not change original values or global value only parameters.

Higher-order functions

• a function take another function as a parameter, e.g. eventListener.
• a function return function as result.

Filter

• filter array based on giving condition and return new array.
• if we want to achieve result of filter we will use for loop nad loop over array then use if statement then push to array then return, it’s called Imperative.

Reduce

• it receive collection or array, and return value based on combine items.

Refactoring JavaScript for Performance and Readability

• functions like map filter reduce etc.. make code more readable and easier to modify or deal with.
• also it reduce code.