docsify/src/core/fetch/ajax.js

/* eslint-disable no-unused-vars */
import progressbar from '../render/progressbar';
import { noop, hasOwn } from '../util/core';

const cache = {};

/**
 * Ajax GET implmentation
 * @param {string} url Resource URL
 * @param {boolean} [hasBar=false] Has progress bar
 * @param {String[]} headers Array of headers
 * @return {Promise} Promise response
 */
export function get(url, hasBar = false, headers = {}) {
  const xhr = new XMLHttpRequest();
  const on = function() {
    xhr.addEventListener.apply(xhr, arguments);
  };

  const cached = cache[url];

  if (cached) {
    return { then: cb => cb(cached.content, cached.opt), abort: noop };
  }

  xhr.open('GET', url);
  for (const i in headers) {
    if (hasOwn.call(headers, i)) {
      xhr.setRequestHeader(i, headers[i]);
    }
  }

  xhr.send();

  return {
    then: function(success, error = noop) {
      if (hasBar) {
        const id = setInterval(
          _ =>
            progressbar({
              step: Math.floor(Math.random() * 5 + 1),
            }),
          500
        );

        on('progress', progressbar);
        on('loadend', evt => {
          progressbar(evt);
          clearInterval(id);
        });
      }

      on('error', error);
      on('load', ({ target }) => {
        if (target.status >= 400) {
          error(target);
        } else {
          const result = (cache[url] = {
            content: target.response,
            opt: {
              updatedAt: xhr.getResponseHeader('last-modified'),
            },
          });

          success(result.content, result.opt);
        }
      });
    },
    abort: _ => xhr.readyState !== 4 && xhr.abort(),
  };
}