Вызов функции.
 

Как записать функцию pipe, чтобы каждая из функций передавала выходные данные другой функции в последовательности?

function isFunction(functionToCheck) {
return functionToCheck && {}.toString.call(functionToCheck) === '[object Function]';
}

const pipe = (value, ...funcs) => {
	
};

const replaceUnderscoreWithSpace = (value) => value.replace(/_/g, ' ');
const capitalize = (value) =>
value
	.split(' ')
        .map((val) => val.charAt(0).toUpperCase() + val.slice(1))
        .join(' ');
const appendGreeting = (value) => `Hello, ${value}!`;

const error = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, '');

alert(error); // Provided argument at position 2 is not a function!

const result = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, appendGreeting);

alert(result); // Hello, John Doe!

OlesiaBOM,

function isFunction(functionToCheck) {
return functionToCheck && {}.toString.call(functionToCheck) === '[object Function]';
}

const pipe = (value, ...funcs) => {
   let [fun, ...f] = funcs, isFun = isFunction(fun);
   value = isFun ? fun(value) : 'error';
   return isFun && f.length ? pipe(value, ...f) : value
};

const replaceUnderscoreWithSpace = (value) => value.replace(/_/g, ' ');
const capitalize = (value) =>
value
    .split(' ')
        .map((val) => val.charAt(0).toUpperCase() + val.slice(1))
        .join(' ');
const appendGreeting = (value) => `Hello, ${value}!`;

const error = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, '');

alert(error); // Provided argument at position 2 is not a function!

const result = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, appendGreeting);

alert(result); // Hello, John Doe!

А так не проще?

const pipe = (value, ...funcs) => {
	try {
		return funcs.reduce ((v, f) => f(v), value)
	} catch (err) {
		return err;
	}
};
 
const replaceUnderscoreWithSpace = (value) => value.replace(/_/g, ' ');
const capitalize = (value) =>
value
    .split(' ')
        .map((val) => val.charAt(0).toUpperCase() + val.slice(1))
        .join(' ');
const appendGreeting = (value) => `Hello, ${value}!`;
 
const error = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, '');
 
alert(error); // Provided argument at position 2 is not a function!
 
const result = pipe('john_doe', replaceUnderscoreWithSpace, capitalize, appendGreeting);
 
alert(result); // Hello, John Doe!