How to refactor an inner setState function into a static class method?

Question

I want to refactor the inner fn of this.setState(fn) to a static method that lives inside the Utils class, Utils.createTargetDict. I cannot wrap my head around how to get the the target parameter's argument from register into my newly created Utils.createTargetDict. I this is a FP technique requires currying but i just cannot figure it out.

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {targets: {}}
  }

  get engine() {
    return {
      state: this.state,
      register: target => {
        this.setState(ps => {
          return {
            targets: {
              ...ps.targets,
              ...Utils.createElement(target),
            },
          };
        });
      },
    }
  }
}

const myComp = new MyComponent();
const engi = myComp.engine;
engi.register({current: {foo: '1', bar: 'a'}});

From:

register: target => {
  this.setState(ps => {
    return {
      targets: {
        ...ps.targets,
        ...Utils.createElement(target),
      },
    };
  });
},

To:

register: target => {
  this.setState(Utils.createTargetDict);
},

Utils

class Utils {
  static createTargetDict(ps) {
    return {
      targets: {
        ...ps.targets,
        ...Utils.createElement(target), // this will fail bc target doesn't exist
      },
    };
  }
  static key() {
    let d, r;
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, c => {
      r = (new Date().getTime() + Math.random() * 16) % 16 | 0;
      d = Math.floor(d / 16);
      return (c === 'x' ? r : (r & 0x3) | 0x8).toString(16);
    });
  }

  static createElement(target) {
    const key = Utils.key();
    return {
      [key]: {
        ...target,
        current: {
          ...target.current,
          key: key,
          visibility: false,
        },
      },
    };
  }
}

[Don't make `Utils` a `class`!](https://stackoverflow.com/q/29893591/1048572) — Bergi, Oct 09 '18 at 18:12

score 1 · Accepted Answer · answered Oct 09 '18 at 18:01

You could wrap the function in closure to do it (notice I've changed the method name slightly to show that we are generating a function):

MyComponent

register: target => {
  this.setState(Utils.getCreateTargetDict(target));
},

Utils

class Utils {
  static getCreateTargetDict(target) {
    return (ps) => {
      return {
        targets: {
          ...ps.targets,
          ...Utils.createElement(target),
        },
      };
    };
  }
}

How to refactor an inner setState function into a static class method?

1 Answers1