error_promise.js

function f() {
    return Math.random() > 0.5 ? 
       	Promise.resolve(10) : 
        Promise.reject(new Error('code x'));
}

function g() {
    return f().then(r => {
        return r + 1;
    }).catch(e => {
    	return new Error('error:' + e.message);
    });
}
  
g()
    .then(r => console.log(r))
    .catch(e => console.error(e));