custom_matchers.js

// jasmine

const customMatchers = {
  toBeArray: function () {
    return {
      compare: function (item) {
        const result = {
          pass: item instanceof Array,
          message: ''
        };

        if(result.pass) {
          result.message = item + ' is instance of Array';
        } else {
          result.message = item + ' is not instance of Array';
        }
        
        return result
      }
    }
  }
};