martianboy/sample.html

## sample.html
<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Page Title</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <style>
    #byte_content {
      margin: 5px 0;
      max-height: 100px;
      overflow-y: auto;
      overflow-x: hidden;
    }

    #byte_range {
      margin-top: 5px;
    }
  </style>
</head>

<body>
  <input type="file" id="files" name="file" /> Read bytes:
  <span class="readBytesButtons">
    <button data-startbyte="0" data-endbyte="4">1-5</button>
    <button data-startbyte="5" data-endbyte="14">6-15</button>
    <button data-startbyte="6" data-endbyte="7">7-8</button>
    <button>entire file</button>
  </span>
  <button type='button' id='validate'>Validate!</button>
  <div id="byte_range"></div>
  <div id="byte_content"></div>

  <script>
    /**
     * Validates a file to be in outlook csv format
     * @param file {File} input file
     * @returns {Promise<boolean>}
     */
    function isValidOutlookFile(file) {
      const OUTLOOK_HEADER_ROW =
        "First Name,Middle Name,Last Name,Title,Suffix,Nickname,Given Yomi,Surname Yomi,E-mail Address,E-mail 2 Address,E-mail 3 Address,Home Phone,Home Phone 2,Business Phone,Business Phone 2,Mobile Phone,Car Phone,Other Phone,Primary Phone,Pager,Business Fax,Home Fax,Other Fax,Company Main Phone,Callback,Radio Phone,Telex,TTY/TDD Phone,IMAddress,Job Title,Department,Company,Office Location,Manager's Name,Assistant's Name,Assistant's Phone,Company Yomi,Business Street,Business City,Business State,Business Postal Code,Business Country/Region,Home Street,Home City,Home State,Home Postal Code,Home Country/Region,Other Street,Other City,Other State,Other Postal Code,Other Country/Region,Personal Web Page,Spouse,Schools,Hobby,Location,Web Page,Birthday,Anniversary,Notes".toLowerCase();

      return new Promise(function (res, rej) {
        if (window.File && window.FileReader && window.FileList && window.Blob) {
          // Take BOM into account
          const headerBlob = file.slice(0, OUTLOOK_HEADER_ROW.length + 3)
          const reader = new FileReader()

          reader.addEventListener('error', rej, false)
          reader.addEventListener('abort', rej, false)

          reader.addEventListener('load', e => {
            /** @type {String} */
            const header = e.target.result
            const result = header.substring(0, OUTLOOK_HEADER_ROW.length).toLowerCase() === OUTLOOK_HEADER_ROW ||
              header.substring(3).toLowerCase() === OUTLOOK_HEADER_ROW

            res(result)
          }, false)

          reader.readAsText(headerBlob)
        }
        else {
          console.warn('Validation impossible!')
          res(true)
        }
      })
    }

    function readBlob(opt_startByte, opt_stopByte) {
      var files = document.getElementById('files').files;
      if (!files.length) {
        alert('Please select a file!');
        return;
      }

      var file = files[0];
      var start = parseInt(opt_startByte) || 0;
      var stop = parseInt(opt_stopByte) || file.size - 1;

      var reader = new FileReader();

      // If we use onloadend, we need to check the readyState.
      reader.onloadend = function (evt) {
        if (evt.target.readyState == FileReader.DONE) { // DONE == 2
          document.getElementById('byte_content').textContent = evt.target.result;
          document.getElementById('byte_range').textContent =
            ['Read bytes: ', start + 1, ' - ', stop + 1,
              ' of ', file.size, ' byte file'].join('');
        }
      };

      var blob = file.slice(start, stop + 1);
      reader.readAsBinaryString(blob);
    }

    function validateFile() {
      var files = document.getElementById('files').files;
      if (!files.length) {
        alert('Please select a file!');
        return;
      }

      var file = files[0];
      isValidOutlookFile(file).then(
        valid => console.log(valid),
        err => console.error(err)
      )
    }

    document.getElementById('validate').addEventListener('click', function(evt) {
      if (evt.target.tagName.toLowerCase() == 'button') {
        var startByte = evt.target.getAttribute('data-startbyte');
        var endByte = evt.target.getAttribute('data-endbyte');
        validateFile()
      }
    }, false)
    document.querySelector('.readBytesButtons').addEventListener('click', function (evt) {
      if (evt.target.tagName.toLowerCase() == 'button') {
        var startByte = evt.target.getAttribute('data-startbyte');
        var endByte = evt.target.getAttribute('data-endbyte');
        readBlob(startByte, endByte);
      }
    }, false);
  </script>
</body>

</html>

## validate.js
/**
 * Validates a file to be in outlook csv format
 * @param file {File} input file
 * @returns {Promise<boolean>}
 */
function isValidOutlookFile(file) {
  const OUTLOOK_HEADER_ROW =
    "First Name,Middle Name,Last Name,Title,Suffix,Nickname,Given Yomi,Surname Yomi,E-mail Address,E-mail 2 Address,E-mail 3 Address,Home Phone,Home Phone 2,Business Phone,Business Phone 2,Mobile Phone,Car Phone,Other Phone,Primary Phone,Pager,Business Fax,Home Fax,Other Fax,Company Main Phone,Callback,Radio Phone,Telex,TTY/TDD Phone,IMAddress,Job Title,Department,Company,Office Location,Manager's Name,Assistant's Name,Assistant's Phone,Company Yomi,Business Street,Business City,Business State,Business Postal Code,Business Country/Region,Home Street,Home City,Home State,Home Postal Code,Home Country/Region,Other Street,Other City,Other State,Other Postal Code,Other Country/Region,Personal Web Page,Spouse,Schools,Hobby,Location,Web Page,Birthday,Anniversary,Notes".toLowerCase();

  return new Promise(function(res, rej) {
    if (window.File && window.FileReader && window.FileList && window.Blob) {
      // Take BOM into account
      const headerBlob = file.slice(0, OUTLOOK_HEADER_ROW.length + 3)
      const reader = new FileReader()

      reader.addEventListener('error', rej, false)
      reader.addEventListener('abort', rej, false)

      reader.addEventListener('load', e => {
        /** @type {String} */
        const header = e.target.result
        const result = header.substring(0, OUTLOOK_HEADER_ROW.length).toLowerCase() === OUTLOOK_HEADER_ROW ||
          header.substring(3).toLowerCase() === OUTLOOK_HEADER_ROW

        res(result)
      }, false)

      reader.readAsText(headerBlob)
    }
    else {
      console.warn('Validation impossible!')
      res(true)
    }
  })
}
	<!DOCTYPE html>
	<html>

	<head>
	<meta charset="utf-8" />
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<title>Page Title</title>
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<style>
	#byte_content {
	margin: 5px 0;
	max-height: 100px;
	overflow-y: auto;
	overflow-x: hidden;
	}

	#byte_range {
	margin-top: 5px;
	}
	</style>
	</head>

	<body>
	<input type="file" id="files" name="file" /> Read bytes:
	<span class="readBytesButtons">
	<button data-startbyte="0" data-endbyte="4">1-5</button>
	<button data-startbyte="5" data-endbyte="14">6-15</button>
	<button data-startbyte="6" data-endbyte="7">7-8</button>
	<button>entire file</button>
	</span>
	<button type='button' id='validate'>Validate!</button>
	<div id="byte_range"></div>
	<div id="byte_content"></div>

	<script>
	/**
	* Validates a file to be in outlook csv format
	* @param file {File} input file
	* @returns {Promise<boolean>}
	*/
	function isValidOutlookFile(file) {
	const OUTLOOK_HEADER_ROW =
	"First Name,Middle Name,Last Name,Title,Suffix,Nickname,Given Yomi,Surname Yomi,E-mail Address,E-mail 2 Address,E-mail 3 Address,Home Phone,Home Phone 2,Business Phone,Business Phone 2,Mobile Phone,Car Phone,Other Phone,Primary Phone,Pager,Business Fax,Home Fax,Other Fax,Company Main Phone,Callback,Radio Phone,Telex,TTY/TDD Phone,IMAddress,Job Title,Department,Company,Office Location,Manager's Name,Assistant's Name,Assistant's Phone,Company Yomi,Business Street,Business City,Business State,Business Postal Code,Business Country/Region,Home Street,Home City,Home State,Home Postal Code,Home Country/Region,Other Street,Other City,Other State,Other Postal Code,Other Country/Region,Personal Web Page,Spouse,Schools,Hobby,Location,Web Page,Birthday,Anniversary,Notes".toLowerCase();

	return new Promise(function (res, rej) {
	if (window.File && window.FileReader && window.FileList && window.Blob) {
	// Take BOM into account
	const headerBlob = file.slice(0, OUTLOOK_HEADER_ROW.length + 3)
	const reader = new FileReader()

	reader.addEventListener('error', rej, false)
	reader.addEventListener('abort', rej, false)

	reader.addEventListener('load', e => {
	/** @type {String} */
	const header = e.target.result
	const result = header.substring(0, OUTLOOK_HEADER_ROW.length).toLowerCase() === OUTLOOK_HEADER_ROW \|\|
	header.substring(3).toLowerCase() === OUTLOOK_HEADER_ROW

	res(result)
	}, false)

	reader.readAsText(headerBlob)
	}
	else {
	console.warn('Validation impossible!')
	res(true)
	}
	})
	}

	function readBlob(opt_startByte, opt_stopByte) {
	var files = document.getElementById('files').files;
	if (!files.length) {
	alert('Please select a file!');
	return;
	}

	var file = files[0];
	var start = parseInt(opt_startByte) \|\| 0;
	var stop = parseInt(opt_stopByte) \|\| file.size - 1;

	var reader = new FileReader();

	// If we use onloadend, we need to check the readyState.
	reader.onloadend = function (evt) {
	if (evt.target.readyState == FileReader.DONE) { // DONE == 2
	document.getElementById('byte_content').textContent = evt.target.result;
	document.getElementById('byte_range').textContent =
	['Read bytes: ', start + 1, ' - ', stop + 1,
	' of ', file.size, ' byte file'].join('');
	}
	};

	var blob = file.slice(start, stop + 1);
	reader.readAsBinaryString(blob);
	}

	function validateFile() {
	var files = document.getElementById('files').files;
	if (!files.length) {
	alert('Please select a file!');
	return;
	}

	var file = files[0];
	isValidOutlookFile(file).then(
	valid => console.log(valid),
	err => console.error(err)
	)
	}

	document.getElementById('validate').addEventListener('click', function(evt) {
	if (evt.target.tagName.toLowerCase() == 'button') {
	var startByte = evt.target.getAttribute('data-startbyte');
	var endByte = evt.target.getAttribute('data-endbyte');
	validateFile()
	}
	}, false)
	document.querySelector('.readBytesButtons').addEventListener('click', function (evt) {
	if (evt.target.tagName.toLowerCase() == 'button') {
	var startByte = evt.target.getAttribute('data-startbyte');
	var endByte = evt.target.getAttribute('data-endbyte');
	readBlob(startByte, endByte);
	}
	}, false);
	</script>
	</body>

	</html>