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Testing DOM Event Handler Implementation in Bootstrap

This test suite validates the EventHandler functionality in Bootstrap’s DOM manipulation module, focusing on event binding, delegation, and handling. It ensures proper event listener management and namespace support across different DOM scenarios.

Test Coverage Overview

The test suite provides comprehensive coverage of EventHandler’s core functionality:

Event listener attachment and removal
Event delegation and bubbling
Namespaced events handling
One-time event binding
Mouse enter/leave event handling
Event property hydration and configuration

Implementation Analysis

The testing approach utilizes Jest’s asynchronous testing capabilities with Promise-based assertions. It implements fixture-based testing patterns, using DOM manipulation to create and clean up test elements. The tests verify both simple and complex event scenarios, including event delegation chains and namespace management.

Technical Details

Testing tools and setup:

Jest test framework
Custom fixture helpers for DOM manipulation
MouseEvent simulation for complex interactions
Jasmine spy implementation for event tracking
Async/Promise-based test execution

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Proper test isolation using beforeAll/afterEach hooks
Comprehensive edge case coverage
Async operation handling
Clear test case organization
Effective use of spies for event verification

twbs/bootstrap

js/tests/unit/dom/event-handler.spec.js

            
import EventHandler from '../../../src/dom/event-handler.js'
import { noop } from '../../../src/util/index.js'
import { clearFixture, getFixture } from '../../helpers/fixture.js'

describe('EventHandler', () => {
  let fixtureEl

  beforeAll(() => {
    fixtureEl = getFixture()
  })

  afterEach(() => {
    clearFixture()
  })

  describe('on', () => {
    it('should not add event listener if the event is not a string', () => {
      fixtureEl.innerHTML = '<div></div>'

      const div = fixtureEl.querySelector('div')

      EventHandler.on(div, null, noop)
      EventHandler.on(null, 'click', noop)

      expect().nothing()
    })

    it('should add event listener', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        const div = fixtureEl.querySelector('div')

        EventHandler.on(div, 'click', () => {
          expect().nothing()
          resolve()
        })

        div.click()
      })
    })

    it('should add namespaced event listener', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        const div = fixtureEl.querySelector('div')

        EventHandler.on(div, 'bs.namespace', () => {
          expect().nothing()
          resolve()
        })

        EventHandler.trigger(div, 'bs.namespace')
      })
    })

    it('should add native namespaced event listener', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        const div = fixtureEl.querySelector('div')

        EventHandler.on(div, 'click.namespace', () => {
          expect().nothing()
          resolve()
        })

        EventHandler.trigger(div, 'click')
      })
    })

    it('should handle event delegation', () => {
      return new Promise(resolve => {
        EventHandler.on(document, 'click', '.test', () => {
          expect().nothing()
          resolve()
        })

        fixtureEl.innerHTML = '<div class="test"></div>'

        const div = fixtureEl.querySelector('div')

        div.click()
      })
    })

    it('should handle mouseenter/mouseleave like the native counterpart', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = [
          '<div class="outer">',
          '<div class="inner">',
          '<div class="nested">',
          '<div class="deep"></div>',
          '</div>',
          '</div>',
          '<div class="sibling"></div>',
          '</div>'
        ].join('')

        const outer = fixtureEl.querySelector('.outer')
        const inner = fixtureEl.querySelector('.inner')
        const nested = fixtureEl.querySelector('.nested')
        const deep = fixtureEl.querySelector('.deep')
        const sibling = fixtureEl.querySelector('.sibling')

        const enterSpy = jasmine.createSpy('mouseenter')
        const leaveSpy = jasmine.createSpy('mouseleave')
        const delegateEnterSpy = jasmine.createSpy('mouseenter')
        const delegateLeaveSpy = jasmine.createSpy('mouseleave')

        EventHandler.on(inner, 'mouseenter', enterSpy)
        EventHandler.on(inner, 'mouseleave', leaveSpy)
        EventHandler.on(outer, 'mouseenter', '.inner', delegateEnterSpy)
        EventHandler.on(outer, 'mouseleave', '.inner', delegateLeaveSpy)

        EventHandler.on(sibling, 'mouseenter', () => {
          expect(enterSpy.calls.count()).toEqual(2)
          expect(leaveSpy.calls.count()).toEqual(2)
          expect(delegateEnterSpy.calls.count()).toEqual(2)
          expect(delegateLeaveSpy.calls.count()).toEqual(2)
          resolve()
        })

        const moveMouse = (from, to) => {
          from.dispatchEvent(new MouseEvent('mouseout', {
            bubbles: true,
            relatedTarget: to
          }))

          to.dispatchEvent(new MouseEvent('mouseover', {
            bubbles: true,
            relatedTarget: from
          }))
        }

        // from outer to deep and back to outer (nested)
        moveMouse(outer, inner)
        moveMouse(inner, nested)
        moveMouse(nested, deep)
        moveMouse(deep, nested)
        moveMouse(nested, inner)
        moveMouse(inner, outer)

        setTimeout(() => {
          expect(enterSpy.calls.count()).toEqual(1)
          expect(leaveSpy.calls.count()).toEqual(1)
          expect(delegateEnterSpy.calls.count()).toEqual(1)
          expect(delegateLeaveSpy.calls.count()).toEqual(1)

          // from outer to inner to sibling (adjacent)
          moveMouse(outer, inner)
          moveMouse(inner, sibling)
        }, 20)
      })
    })
  })

  describe('one', () => {
    it('should call listener just once', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        let called = 0
        const div = fixtureEl.querySelector('div')
        const obj = {
          oneListener() {
            called++
          }
        }

        EventHandler.one(div, 'bootstrap', obj.oneListener)

        EventHandler.trigger(div, 'bootstrap')
        EventHandler.trigger(div, 'bootstrap')

        setTimeout(() => {
          expect(called).toEqual(1)
          resolve()
        }, 20)
      })
    })

    it('should call delegated listener just once', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'

        let called = 0
        const div = fixtureEl.querySelector('div')
        const obj = {
          oneListener() {
            called++
          }
        }

        EventHandler.one(fixtureEl, 'bootstrap', 'div', obj.oneListener)

        EventHandler.trigger(div, 'bootstrap')
        EventHandler.trigger(div, 'bootstrap')

        setTimeout(() => {
          expect(called).toEqual(1)
          resolve()
        }, 20)
      })
    })
  })

  describe('off', () => {
    it('should not remove a listener', () => {
      fixtureEl.innerHTML = '<div></div>'
      const div = fixtureEl.querySelector('div')

      EventHandler.off(div, null, noop)
      EventHandler.off(null, 'click', noop)
      expect().nothing()
    })

    it('should remove a listener', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let called = 0
        const handler = () => {
          called++
        }

        EventHandler.on(div, 'foobar', handler)
        EventHandler.trigger(div, 'foobar')

        EventHandler.off(div, 'foobar', handler)
        EventHandler.trigger(div, 'foobar')

        setTimeout(() => {
          expect(called).toEqual(1)
          resolve()
        }, 20)
      })
    })

    it('should remove all the events', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let called = 0

        EventHandler.on(div, 'foobar', () => {
          called++
        })
        EventHandler.on(div, 'foobar', () => {
          called++
        })
        EventHandler.trigger(div, 'foobar')

        EventHandler.off(div, 'foobar')
        EventHandler.trigger(div, 'foobar')

        setTimeout(() => {
          expect(called).toEqual(2)
          resolve()
        }, 20)
      })
    })

    it('should remove all the namespaced listeners if namespace is passed', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let called = 0

        EventHandler.on(div, 'foobar.namespace', () => {
          called++
        })
        EventHandler.on(div, 'foofoo.namespace', () => {
          called++
        })
        EventHandler.trigger(div, 'foobar.namespace')
        EventHandler.trigger(div, 'foofoo.namespace')

        EventHandler.off(div, '.namespace')
        EventHandler.trigger(div, 'foobar.namespace')
        EventHandler.trigger(div, 'foofoo.namespace')

        setTimeout(() => {
          expect(called).toEqual(2)
          resolve()
        }, 20)
      })
    })

    it('should remove the namespaced listeners', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let calledCallback1 = 0
        let calledCallback2 = 0

        EventHandler.on(div, 'foobar.namespace', () => {
          calledCallback1++
        })
        EventHandler.on(div, 'foofoo.namespace', () => {
          calledCallback2++
        })

        EventHandler.trigger(div, 'foobar.namespace')
        EventHandler.off(div, 'foobar.namespace')
        EventHandler.trigger(div, 'foobar.namespace')

        EventHandler.trigger(div, 'foofoo.namespace')

        setTimeout(() => {
          expect(calledCallback1).toEqual(1)
          expect(calledCallback2).toEqual(1)
          resolve()
        }, 20)
      })
    })

    it('should remove the all the namespaced listeners for native events', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let called = 0

        EventHandler.on(div, 'click.namespace', () => {
          called++
        })
        EventHandler.on(div, 'click.namespace2', () => {
          called++
        })

        EventHandler.trigger(div, 'click')
        EventHandler.off(div, 'click')
        EventHandler.trigger(div, 'click')

        setTimeout(() => {
          expect(called).toEqual(2)
          resolve()
        }, 20)
      })
    })

    it('should remove the specified namespaced listeners for native events', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = '<div></div>'
        const div = fixtureEl.querySelector('div')

        let called1 = 0
        let called2 = 0

        EventHandler.on(div, 'click.namespace', () => {
          called1++
        })
        EventHandler.on(div, 'click.namespace2', () => {
          called2++
        })
        EventHandler.trigger(div, 'click')

        EventHandler.off(div, 'click.namespace')
        EventHandler.trigger(div, 'click')

        setTimeout(() => {
          expect(called1).toEqual(1)
          expect(called2).toEqual(2)
          resolve()
        }, 20)
      })
    })

    it('should remove a listener registered by .one', () => {
      return new Promise((resolve, reject) => {
        fixtureEl.innerHTML = '<div></div>'

        const div = fixtureEl.querySelector('div')
        const handler = () => {
          reject(new Error('called'))
        }

        EventHandler.one(div, 'foobar', handler)
        EventHandler.off(div, 'foobar', handler)

        EventHandler.trigger(div, 'foobar')
        setTimeout(() => {
          expect().nothing()
          resolve()
        }, 20)
      })
    })

    it('should remove the correct delegated event listener', () => {
      const element = document.createElement('div')
      const subelement = document.createElement('span')
      element.append(subelement)

      const anchor = document.createElement('a')
      element.append(anchor)

      let i = 0
      const handler = () => {
        i++
      }

      EventHandler.on(element, 'click', 'a', handler)
      EventHandler.on(element, 'click', 'span', handler)

      fixtureEl.append(element)

      EventHandler.trigger(anchor, 'click')
      EventHandler.trigger(subelement, 'click')

      // first listeners called
      expect(i).toEqual(2)

      EventHandler.off(element, 'click', 'span', handler)
      EventHandler.trigger(subelement, 'click')

      // removed listener not called
      expect(i).toEqual(2)

      EventHandler.trigger(anchor, 'click')

      // not removed listener called
      expect(i).toEqual(3)

      EventHandler.on(element, 'click', 'span', handler)
      EventHandler.trigger(anchor, 'click')
      EventHandler.trigger(subelement, 'click')

      // listener re-registered
      expect(i).toEqual(5)

      EventHandler.off(element, 'click', 'span')
      EventHandler.trigger(subelement, 'click')

      // listener removed again
      expect(i).toEqual(5)
    })
  })

  describe('general functionality', () => {
    it('should hydrate properties, and make them configurable', () => {
      return new Promise(resolve => {
        fixtureEl.innerHTML = [
          '<div id="div1">',
          '   <div id="div2"></div>',
          '   <div id="div3"></div>',
          '</div>'
        ].join('')

        const div1 = fixtureEl.querySelector('#div1')
        const div2 = fixtureEl.querySelector('#div2')

        EventHandler.on(div1, 'click', event => {
          expect(event.currentTarget).toBe(div2)
          expect(event.delegateTarget).toBe(div1)
          expect(event.originalTarget).toBeNull()

          Object.defineProperty(event, 'currentTarget', {
            configurable: true,
            get() {
              return div1
            }
          })

          expect(event.currentTarget).toBe(div1)
          resolve()
        })

        expect(() => {
          EventHandler.trigger(div1, 'click', { originalTarget: null, currentTarget: div2 })
        }).not.toThrowError(TypeError)
      })
    })
  })
})