bootstrap-vue/src/components/table/helpers/default-sort-compare.js

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import { get } from '../../../utils/get'
import { isDate, isFunction, isNumber, isNumeric, isUndefinedOrNull } from '../../../utils/inspect'
import { toFloat } from '../../../utils/number'
import { stringifyObjectValues } from '../../../utils/stringify-object-values'

const normalizeValue = value => {
  if (isUndefinedOrNull(value)) {
    return ''
  }
  if (isNumeric(value)) {
    return toFloat(value, value)
  }
  return value
}

// Default sort compare routine
//
// TODO:
//   Add option to sort by multiple columns (tri-state per column,
//   plus order of columns in sort) where `sortBy` could be an array
//   of objects `[ {key: 'foo', sortDir: 'asc'}, {key:'bar', sortDir: 'desc'} ...]`
//   or an array of arrays `[ ['foo','asc'], ['bar','desc'] ]`
//   Multisort will most likely be handled in `mixin-sort.js` by
//   calling this method for each sortBy
export const defaultSortCompare = (
  a,
  b,
  { sortBy = null, formatter = null, locale = undefined, localeOptions = {}, nullLast = false } = {}
) => {
  // Get the value by `sortBy`
  let aa = get(a, sortBy, null)
  let bb = get(b, sortBy, null)

  // Apply user-provided formatter
  if (isFunction(formatter)) {
    aa = formatter(aa, sortBy, a)
    bb = formatter(bb, sortBy, b)
  }

  // Internally normalize value
  // `null` / `undefined` => ''
  // `'0'` => `0`
  aa = normalizeValue(aa)
  bb = normalizeValue(bb)

  if ((isDate(aa) && isDate(bb)) || (isNumber(aa) && isNumber(bb))) {
    // Special case for comparing dates and numbers
    // Internally dates are compared via their epoch number values
    return aa < bb ? -1 : aa > bb ? 1 : 0
  } else if (nullLast && aa === '' && bb !== '') {
    // Special case when sorting `null` / `undefined` / '' last
    return 1
  } else if (nullLast && aa !== '' && bb === '') {
    // Special case when sorting `null` / `undefined` / '' last
    return -1
  }

  // Do localized string comparison
  return stringifyObjectValues(aa).localeCompare(stringifyObjectValues(bb), locale, localeOptions)
}