index.js

/* Node.js 6.4.0 and up has full support */
var hasFullSupport = (function () {
  try {
    if (!Buffer.isEncoding('latin1')) {
      return false
    }

    var buf = Buffer.alloc ? Buffer.alloc(4) : new Buffer(4)

    buf.fill('ab', 'ucs2')

    return (buf.toString('hex') === '61006200')
  } catch (_) {
    return false
  }
}())

function isSingleByte (val) {
  return (val.length === 1 && val.charCodeAt(0) < 256)
}

function fillWithNumber (buffer, val, start, end) {
  if (start < 0 || end > buffer.length) {
    throw new RangeError('Out of range index')
  }

  start = start >>> 0
  end = end === undefined ? buffer.length : end >>> 0

  if (end > start) {
    buffer.fill(val, start, end)
  }

  return buffer
}

function fillWithBuffer (buffer, val, start, end) {
  if (start < 0 || end > buffer.length) {
    throw new RangeError('Out of range index')
  }

  if (end <= start) {
    return buffer
  }

  start = start >>> 0
  end = end === undefined ? buffer.length : end >>> 0

  var pos = start
  var len = val.length
  while (pos <= (end - len)) {
    val.copy(buffer, pos)
    pos += len
  }

  if (pos !== end) {
    val.copy(buffer, pos, 0, end - pos)
  }

  return buffer
}

function fill (buffer, val, start, end, encoding) {
  if (hasFullSupport) {
    return buffer.fill(val, start, end, encoding)
  }

  if (typeof val === 'number') {
    return fillWithNumber(buffer, val, start, end)
  }

  if (typeof val === 'string') {
    if (typeof start === 'string') {
      encoding = start
      start = 0
      end = buffer.length
    } else if (typeof end === 'string') {
      encoding = end
      end = buffer.length
    }

    if (encoding !== undefined && typeof encoding !== 'string') {
      throw new TypeError('encoding must be a string')
    }

    if (encoding === 'latin1') {
      encoding = 'binary'
    }

    if (typeof encoding === 'string' && !Buffer.isEncoding(encoding)) {
      throw new TypeError('Unknown encoding: ' + encoding)
    }

    if (val === '') {
      return fillWithNumber(buffer, 0, start, end)
    }

    if (isSingleByte(val)) {
      return fillWithNumber(buffer, val.charCodeAt(0), start, end)
    }

    val = new Buffer(val, encoding)
  }

  if (Buffer.isBuffer(val)) {
    return fillWithBuffer(buffer, val, start, end)
  }

  // Other values (e.g. undefined, boolean, object) results in zero-fill
  return fillWithNumber(buffer, 0, start, end)
}

module.exports = fill