react-loop-item

A simple component that repeatedly creates components.

Usage no npm install needed!

<script type="module">
  import reactLoopItem from 'https://cdn.skypack.dev/react-loop-item';
</script>

README

react-loop-item

A simple component that repeatedly creates components.

NPM JavaScript Style Guide

Install

npm install react-loop-item --save

or

yarn add react-loop-item

Usage

LoopItem component

import { LoopItem } from "react-loop-item";
// or
// import LoopItem from 'react-loop-item";

const Articles = () => {
  // [list]: <Item> props
  const itemProps = [
    { contents: "1. Article sample A" },
    { contents: "2. Article sample B" },
  ];

  return <LoopItem target={Item} list={itemProps} />;
};

// [target]: item component of list
const Item = ({ contents }) => <p>{contents}</p>;

ListWrap component

[version] ^1.1.0

import { ListWrap } from "react-loop-item";

const Articles = () => {
  // [list]: <Item> props
  const itemProps = [
    { contents: "1. Article sample A" },
    { contents: "2. Article sample B" },
  ];

  return (
    <ListWrap
      // list tag
      tag="ul"
      className="ul-class"
      data-description="add any ul attributes"
      // LoopItem props
      target={Item}
      list={itemProps}
    />
  );
};

// [target]: item component of list
const Item = ({ contents }) => <li>{contents}</li>;

loop method

import { LoopItem, loop } from "react-loop-item";

loop(Item, list, each, instead, hidden, memo);
//or
<LoopItem
  target={Item}
  list={arr}
  each={fnc}
  instead={element}
  hidden={boolean}
  memo={boolean}
/>;

Props

target (required)

[type] elementType(React.Component, React.FC, React.forwardRef, string)

Component to be created repeatedly.

// component
<LoopItem target={ItemComponent} />;
// or tag name
<LoopItem target={"img"} />;

list (optional)

[type] Array | number

Item data array or number of items.

// array
<LoopItem target={Item} list={[{ foo: "bar" }, { foo: "bar" }]} />;
// or count
<LoopItem target={Item} list={5} />;

each (optional)

[type] Function

Callback function that converts each element of list to props for target when rendering target component. If each is omitted, list element is used as it is.

each has two arguments. (element and index of list)

// [list]: raw datas
const model = [{ foo: "bar" }, { foo: "bar" }];

// [each]: formatter for <Anchor> props
const getProps = (data, index) => ({
  // properties
  value: data.foo,
  // callbacks
  onClick: (event) => {
    event.preventDefault();
    console.log(model, data, index);
  },
});

// [target]: <Ancher> has value and onClick
const Anchor = ({ value, onClick }) => (
  <a href="#" onClick={onClick}>
    {value}
  </a>
);

<LoopItem target={Anchor} list={model} each={getProps} />;

tag (optional)

[type] string, [version] ^1.1.0, [for] ListWrap

Set tag name of parent element to wrap items.

<ListWrap tag="div" className="tag-example" target={item} list={model}> />
// or
<div className="tag-example">
  <LoopItem target={Child} list={model}>
</div>

instead (optional)

[type] React.ReactNode

Element to return instead of null when list is empty. Use strings or element, no component.

target={Component} instead={strings or element}

// [list] : no data
const model = [];

// [instead]: element to render instead of blank
const noData = <span>no data</span>;

// do not use component
// const noData = () => <span>no data</span>;

<LoopItem target={Item} list={model} instead={noData} />;

hidden (optional)

[type] boolean

Prevent rendering.

<LoopItem target={Item} list={model} hidden />
// or
<LoopItem target={Item} list={model} hidden={true} />

memo (optional)

[type] string | boolean, [version] ^1.1.2

Whether to cache target using React.memo.

To use this feature, enter prop name of target you want to use as key in list, or true. Use it when absolutely necessary. Frequent use of React.memo is not recommended.

<LoopItem target={Item} list={model} memo="id" />
// or
<LoopItem target={Item} list={model} memo={true} />

Examples

AnchorList.jsx

import React from "react";
import { ListWrap } from "react-loop-item";

import style from "./AnchorList.module.css";

// <AnchorList> needs raw data array and <Item> props formatter.
const AnchorList = ({ list, each }) => (
  <ListWrap
    tag="ul"
    className={style["ul-style"]}
    target={Item}
    list={list}
    each={each}
    instead={noData}
  />
);

// check target props
const Item = ({ label, href, onClick }) => (
  <li className={style["li-style"]}>
    <a href={href} onClick={onClick}>
      {label}
    </a>
  </li>
);

// what to display instead of the <ul>
const noData = <div>no data</div>;

export default AnchorList;

Tags.jsx

import React from "react";
import { LoopItem } from "react-loop-item";

import style from "./Tags.module.css";

// if you already know about raw datas,
// define <Item> props formatter in this component.
const Tags = ({ list }) => (
  <p className={style["p-style"]}>
    <LoopItem target={Item} list={list} each={getProps} />
  </p>
);

const Item = ({ value }) => (
  <span className={style["span-style"]}>{value}</span>
);

// convert string to <Item> props
const getProps = (text, index) => ({
  value: text,
});

export default Tags;

ListContainer.jsx

import React from "react";
import AnchorList from "./AnchorList";
import Tags from "./Tags";

const ListContainer = () => {
  // <AnchorList> raw datas
  const siteList = [
    { url: "aaa.com", description: "aaa site", visited: 4 },
    { url: "bbb.com", description: "bbb site", visited: 2 },
    { url: "ccc.com", description: "ccc site", visited: 8 },
  ];

  // formatter for <Item> props of <AnchorList>
  const getProps = (data, index) => {
    // raw datas (element and index of siteList)
    const { url, description, visited } = data;

    // props
    return {
      key: url, // if key is omitted, index is used
      label: description,
      href: url,
      onClick(event) {
        event.preventDefault();
        console.log(siteList, index, visited);
      },
    };
  };

  // <Tags> raw datas
  const tagList = ["react", "loop", "for", "each", "list"];

  return (
    <div>
      {/* your components */}
      <AnchorList list={siteList} each={getProps} />
      <Tags list={tagList} />
    </div>
  );
};

export default ListContainer;

Tips

Injecting Callbacks

If the structure of the raw data is fixed, the component using LoopItem defines props a formatter for the list item component. Then use the parent component's state or props to develop functions to use as callback.

import React from "react";
import AnchorList from "./AnchorList";

const ListContainer = () => {
  // code to manage model
  // ...

  const updateVisited = (url, count) => {
    // do something for updating model
  };

  // callbacks injector for <Item> of <AnchorList>
  const getItemCallbacks = (data, index) => {
    const { url, description, visited } = data;

    // callbacks
    return {
      onClick(event) {
        event.preventDefault();

        // update visited
        updateVisited(url, visited + 1);
      },
    };
  };

  return (
    <div>
      {/* your component */}
      <AnchorList list={model} each={getItemCallbacks} />
    </div>
  );
};

export default ListContainer;

import React from "react";
import { LoopItem } from "react-loop-item";

import style from "./AnchorList.module.css";

// <AnchorList> needs raw datas and <Item> callbacks injector.
const AnchorList = ({ list, each }) => {
  // formatter for <Item> props
  const getItemProps = (data, index) => {
    const { url, description, visited } = data;

    return {
      // properties
      key: url,
      href: url,
      label: description,

      // inject <Item> callbacks
      ...each(data, index),
    };
  };

  return (
    <ul className={style["ul-style"]}>
      <LoopItem target={Item} list={list} each={getItemProps} />
    </ul>
  );
};

// check target props
const Item = ({ label, href, onClick }) => (
  <li className={style["li-style"]}>
    <a href={href} onClick={onClick}>
      {label}
    </a>
  </li>
);

export default AnchorList;

Rendering Optimization

If rendering optimization is required, set the memo option.

For this to work smoothly, you need to manage the elements of the list as immutable objects. And make sure the references to the each callback don't change.

import React, { useReducer, useCallback } from "react";
import { ListWrap } from "react-loop-item";

// demo data
const siteList = [
  { url: "aaa.com", description: "aaa site", visited: 4 },
  { url: "bbb.com", description: "bbb site", visited: 2 },
  { url: "ccc.com", description: "ccc site", visited: 8 },
];

// list reducer
const reducer = (state, url) =>
  state.map((item) =>
    // returns new object only if it is a target.
    item.url !== url
      ? item
      : {
          ...item,
          visited: item.visited + 1,
        }
  );

const MemoList = () => {
  // visit is dispatch
  const [list, visit] = useReducer(reducer, siteList);

  // cached each
  const each = useCallback(
    (data, index) => ({
      ...data,
      onClick(event) {
        event.preventDefault();
        visit(data.url);
      },
    }),
    [visit] // visit does not change the reference
  );

  // try changing memo
  return <ListWrap tag="ul" target={Anchor} list={list} each={each} memo />;
};

const Anchor = ({ url, description, visited, onClick }) => {
  // check rendering
  console.log("rendering!", url);
  return (
    <li>
      <a href={url} onClick={onClick}>
        {description}({visited})
      </a>
    </li>
  );
};

export default MemoList;

License

MIT © coxcore