new-character.js

let character = {};
updateCharacter = (path, value) => {
   character[path] = value;
}

const Character = function() {
   this.moves = [];
   this.firstName = ''
   this.lastName = ''
   
   this.getName = () => `${this.firstName} ${this.lastName}`;
   this.setFirstName = name => this.firstName = name;
   this.setLastName = name => this.lastName = name;

   this.addMove = (name, notatian) => {
      this.moves.push({ name, notatian });
   }

   this.toString = () => JSON.stringify({
      name: this.getName(),
      firstName: this.firstName,
      lastName: this.lastName,
      moves: this.moves,
   })
};

const cassieCage = new Character();
[
{
   name: 'Cassie'
},
{
   name: 'Cage'
},
{
   header: 'normals'
},
{
   Rollin: 'F1'
}
].reduce((accumulator, current, index) => {
   if(index === 0) {
      cassieCage.setFirstName(current.name);
   }
   if(index === 1) {
      cassieCage.setLastName(current.name);
   }
   if(index > 2) {
      let [name] = Object.keys(current);
      cassieCage.addMove(name, current[name]);
   }
   console.log(accumulator)

   return accumulator.concat(current);
}, []);

console.log(cassieCage.toString()) // {"name":"Cassie Cage","firstName":"Cassie","lastName":"Cage","moves":[{"name":"Rollin","notatian":"F1"}]}