How to log the program flow of a very deep and complex functional JavaScript code? -

i'm trying understand flow of functions in reselect library. use console.log log output. still, hard understand flow. make me think how complex functional programming is!!!

how can intercept calls , log function name , parameters console es6 decorator or proxy or other language features?

function defaultequalitycheck(a, b) {    return === b  }    function areargumentsshallowlyequal(equalitycheck, prev, next) {    if (prev === null || next === null || prev.length !== next.length) {      return false    }      // in loop (and not `foreach` or `every`) can determine equality fast possible.    const length = prev.length    (let = 0; < length; i++) {      if (!equalitycheck(prev[i], next[i])) {        return false      }    }      return true  }    function defaultmemoize(func, equalitycheck = defaultequalitycheck) {        let lastargs = null    let lastresult = null        console.log("entering defaultmemoize");        console.log("###input### defaultmemoize argument func type: " + typeof func);        // reference arguments instead of spreading them performance reasons    return function () {            if (!areargumentsshallowlyequal(equalitycheck, lastargs, arguments)) {                // apply arguments instead of spreading performance.        lastresult = func.apply(null, arguments)      }        lastargs = arguments            return lastresult    }  }    function getdependencies(funcs) {    const dependencies = array.isarray(funcs[0]) ? funcs[0] : funcs      if (!dependencies.every(dep => typeof dep === 'function')) {      const dependencytypes = dependencies.map(        dep => typeof dep      ).join(', ')      throw new error(        'selector creators expect input-selectors functions, ' +        `instead received following types: [${dependencytypes}]`      )    }      return dependencies  }    function createselectorcreator(memoize, ...memoizeoptions) {        console.log("entering createselectorcreator");        console.log("#input# argument memoize name: " + memoize.name);      console.log("#input# argument memoize options: ");        console.log(memoizeoptions);      return (...funcs) => {            let recomputations = 0            const resultfunc = funcs.pop()      const dependencies = getdependencies(funcs)        console.log("##input## argument funcs: ");      console.log(resultfunc);            const memoizedresultfunc = memoize(        function () {          recomputations++                    // apply arguments instead of spreading performance.          return resultfunc.apply(null, arguments)        },        ...memoizeoptions      )            console.log("memoizedresultfunc: " + typeof memoizedresultfunc);        // if selector called exact same arguments don't need traverse our dependencies again.      const selector = defaultmemoize(function () {        const params = []        const length = dependencies.length          if (arguments != null)        {          console.log("***input*** arguments: ");          console.log(arguments);        }                (let = 0; < length; i++) {          // apply arguments instead of spreading , mutate local list of params performance.          params.push(dependencies[i].apply(null, arguments))        }          // apply arguments instead of spreading performance.        return memoizedresultfunc.apply(null, params)      })        selector.resultfunc = resultfunc      selector.recomputations = () => recomputations      selector.resetrecomputations = () => recomputations = 0            return selector    }  }    const createselector = createselectorcreator(defaultmemoize)    function createstructuredselector(selectors, selectorcreator = createselector) {    if (typeof selectors !== 'object') {      throw new error(        'createstructuredselector expects first argument object ' +        `where each property selector, instead received ${typeof selectors}`      )    }    const objectkeys = object.keys(selectors)    return selectorcreator(      objectkeys.map(key => selectors[key]),      (...values) => {        return values.reduce((composition, value, index) => {          composition[objectkeys[index]] = value          return composition        }, {})      }    )  }    const shopitemsselector = state => state.shop.items  const taxpercentselector = state => state.shop.taxpercent    const subtotalselector = createselector(    shopitemsselector,    items => items.reduce((acc, item) => acc + item.value, 0)  )    const taxselector = createselector(    subtotalselector,    taxpercentselector,    (subtotal, taxpercent) => subtotal * (taxpercent / 100)  )    const totalselector = createselector(    subtotalselector,    taxselector,    (subtotal, tax) => ({ total: subtotal + tax })  )    let examplestate = {    shop: {      taxpercent: 8,      items: [        { name: 'apple', value: 1.20 },        { name: 'orange', value: 0.95 },      ]    }  }    console.log(subtotalselector(examplestate))// 2.15  //console.log(taxselector(examplestate))// 0.172  //console.log(totalselector(examplestate))// { total: 2.322 }