Generic way to detect if html form is edited

Question

I have a tabbed html form. Upon navigating from one tab to the other, the current tab\'s data is persisted (on the DB) even if there is no change to the data.

I woul

Answer 1

Here's a polyfill method demo in native JavaScript that uses the FormData() API to detect created, updated, and deleted form entries. You can check if anything was changed using HTMLFormElement#isChanged and get an object containing the differences from a reset form using HTMLFormElement#changes (assuming they're not masked by an input name):

Object.defineProperties(HTMLFormElement.prototype, {
  isChanged: {
    configurable: true,
    get: function isChanged () {
      'use strict'

      var thisData = new FormData(this)
      var that = this.cloneNode(true)

      // avoid masking: https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/reset
      HTMLFormElement.prototype.reset.call(that)

      var thatData = new FormData(that)

      const theseKeys = Array.from(thisData.keys())
      const thoseKeys = Array.from(thatData.keys())

      if (theseKeys.length !== thoseKeys.length) {
        return true
      }

      const allKeys = new Set(theseKeys.concat(thoseKeys))

      function unequal (value, index) {
        return value !== this[index]
      }

      for (const key of theseKeys) {
        const theseValues = thisData.getAll(key)
        const thoseValues = thatData.getAll(key)

        if (theseValues.length !== thoseValues.length) {
          return true
        }

        if (theseValues.some(unequal, thoseValues)) {
          return true
        }
      }

      return false
    }
  },
  changes: {
    configurable: true,
    get: function changes () {
      'use strict'

      var thisData = new FormData(this)
      var that = this.cloneNode(true)

      // avoid masking: https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/reset
      HTMLFormElement.prototype.reset.call(that)

      var thatData = new FormData(that)

      const theseKeys = Array.from(thisData.keys())
      const thoseKeys = Array.from(thatData.keys())

      const created = new FormData()
      const deleted = new FormData()
      const updated = new FormData()

      const allKeys = new Set(theseKeys.concat(thoseKeys))

      function unequal (value, index) {
        return value !== this[index]
      }

      for (const key of allKeys) {
        const theseValues = thisData.getAll(key)
        const thoseValues = thatData.getAll(key)

        const createdValues = theseValues.slice(thoseValues.length)
        const deletedValues = thoseValues.slice(theseValues.length)

        const minLength = Math.min(theseValues.length, thoseValues.length)

        const updatedValues = theseValues.slice(0, minLength).filter(unequal, thoseValues)

        function append (value) {
          this.append(key, value)
        }

        createdValues.forEach(append, created)
        deletedValues.forEach(append, deleted)
        updatedValues.forEach(append, updated)
      }

      return {
        created: Array.from(created),
        deleted: Array.from(deleted),
        updated: Array.from(updated)
      }
    }
  }
})

document.querySelector('[value="Check"]').addEventListener('click', function () {
  if (this.form.isChanged) {
    console.log(this.form.changes)
  } else {
    console.log('unchanged')
  }
})

  

    Text Input:
    
  

  

    
Radio Button Choice

    Choice 1
    

    Choice 2
    
  

  

    Select Dropdown Choice:
    
      Choice 1
      Choice 2
      Choice 3
    
  

  

    Textarea:
    
  

  

    Checkbox: