attribute-utils.ts

// Utilities for processing HTML element attributes
import { ElementRef } from '@angular/core';

export interface AttrMap {
  [key: string]: string;
}

/**
 * Get attribute map from element or ElementRef `attributes`.
 * Attribute map keys are forced lowercase for case-insensitive lookup.
 * @param el The source of the attributes.
 */
export function getAttrs(el: HTMLElement | ElementRef): AttrMap {
  const attrs: NamedNodeMap = el instanceof ElementRef ? el.nativeElement.attributes : el.attributes;
  const attrMap: AttrMap = {};
  for (const attr of attrs as any as Attr[] /* cast due to https://github.com/Microsoft/TypeScript/issues/2695 */) {
    attrMap[attr.name.toLowerCase()] = attr.value;
  }
  return attrMap;
}

/**
 * Return the attribute that matches `attr`.
 * @param attr Name of the attribute or a string of candidate attribute names.
 */
export function getAttrValue(attrs: AttrMap, attr: string | string[]): string | undefined {
  const key = (typeof attr === 'string')
      ? attr
      : attr.find(a => attrs.hasOwnProperty(a.toLowerCase()));

  return (key === undefined) ? undefined : attrs[key.toLowerCase()];
}

/**
 * Return the boolean state of an attribute value (if supplied)
 * @param attrValue The string value of some attribute (or undefined if attribute not present).
 * @param def Default boolean value when attribute is undefined.
 */
export function boolFromValue(attrValue: string | undefined, def: boolean = false) {
  return attrValue === undefined ? def : attrValue.trim() !== 'false';
}

/**
 * Return the boolean state of attribute from an element
 * @param el The source of the attributes.
 * @param atty Name of the attribute or a string of candidate attribute names.
 * @param def Default boolean value when attribute is undefined.
 */
export function getBoolFromAttribute(
  el: HTMLElement | ElementRef,
  attr: string | string[],
  def: boolean = false): boolean {
  return boolFromValue(getAttrValue(getAttrs(el), attr), def);
}