lots of important stuff (#1883)

* lots of important stuff

* Update Constants.js

src/rest/DiscordAPIError.js

@@ -0,0 +1,54 @@
+/**
+ * Represents an error from the Discord API.
+ * @extends Error
+ */
+class DiscordAPIError extends Error {
+  constructor(path, error) {
+    super();
+    const flattened = this.constructor.flattenErrors(error.errors || error).join('\n');
+    this.name = 'DiscordAPIError';
+    this.message = error.message && flattened ? `${error.message}\n${flattened}` : error.message || flattened;
+
+    /**
+     * The path of the request relative to the HTTP endpoint
+     * @type {string}
+     */
+    this.path = path;
+
+    /**
+     * HTTP error code returned by Discord
+     * @type {number}
+     */
+    this.code = error.code;
+  }
+
+  /**
+   * Flattens an errors object returned from the API into an array.
+   * @param {Object} obj Discord errors object
+   * @param {string} [key] Used internally to determine key names of nested fields
+   * @returns {string[]}
+   * @private
+   */
+  static flattenErrors(obj, key = '') {
+    let messages = [];
+
+    for (const [k, v] of Object.entries(obj)) {
+      if (k === 'message') continue;
+      const newKey = key ? isNaN(k) ? `${key}.${k}` : `${key}[${k}]` : k;
+
+      if (v._errors) {
+        messages.push(`${newKey}: ${v._errors.map(e => e.message).join(' ')}`);
+      } else if (v.code || v.message) {
+        messages.push(`${v.code ? `${v.code}: ` : ''}${v.message}`.trim());
+      } else if (typeof v === 'string') {
+        messages.push(v);
+      } else {
+        messages = messages.concat(this.flattenErrors(v, newKey));
+      }
+    }
+
+    return messages;
+  }
+}
+
+module.exports = DiscordAPIError;