composePipeChain.js

var _ = require('lodash');

class Formatter{
    constructor(repetitions){
        this.repetitions = repetitions;
    }

    format1(txt){
        return `${"[" .repeat(this.repetitions)} ${txt} ${"]" .repeat(this.repetitions)}`;
    }

    format2(txt){
        return `${"(" .repeat(this.repetitions)} ${txt} ${")" .repeat(this.repetitions)}`;
    }
}

let cities = [
    "Paris",
    null,
    "Toulouse",
    "Xixon",
    "",
    "Berlin"
];

let result = _.reverse(
    _.take(
        _.compact(cities)
        , 3
    )
);

console.log(result);
console.log("------------------");

result = _.flow([
    _.compact,
    (ar) => _.take(ar, 3),
    _.reverse
])(cities);

console.log(result);
console.log("------------------");

result = _.chain(cities)
    .compact()
    .take(3)
    .reverse()
    .value();

console.log(result);
console.log("------------------");
 
//when composing methods, we'll need to provide the right "this" value
let formatter = new Formatter(2);

//here we're missing the "this"
let formatFn = _.flow([
    formatter.format1,
    formatter.format2
]);

console.log(formatFn("hi"));
// hi
console.log("------------------");

//_.flow will pass as "this" to each function the "this" bound to the created function, so let's do a bind:
let boundFormatFn = formatFn.bind(formatter);
console.log(boundFormatFn("hi"));
// (( [[ hi ]] ))
console.log("------------------");

//if _.flow were not providing that feature, we could create wrapping functions for each method call
let formatFn2 = _.flow([
    (st) => formatter.format1(st),
    (st) => formatter.format2(st)
]);
console.log(formatFn2("hi"));
//(( [[ hi ]] ))
console.log("------------------");

//or call bind in each method-function being composed:
let formatFn3 = _.flow([
    formatter.format1.bind(formatter),
    formatter.format2.bind(formatter)
]);
console.log(formatFn3("hi"));
//(( [[ hi ]] ))
console.log("------------------");