expand-contractions/lib/contractions.js

Convert English word contractions such "what's" into "what is".

'use strict';

var wordLookup = require('./word-lookup');

class Contractions {
  constructor(contractions) {
    var keys;

    this._expandLookup = contractions;
    // Put the longest keys first so they match before shorter, partial matches.
    keys = Object.keys(this._expandLookup);
    keys.sort((a, b) => {
      var diff = b.length - a.length;

      if (diff !== 0) diff = this._expandLookup[b].length - this._expandLookup[a].length;

      return diff;
    });
    this._expandRegexp = new RegExp(keys.join('|'), 'gi');

    // Build reverse lookup
    let contractLookup = {};

    Object.keys(contractions).forEach(function (key) {
      contractLookup[contractions[key]] = key;
    });

    this._contractLookup = contractLookup;
    keys = Object.keys(this._contractLookup);
    keys.sort((a, b) => {
      var diff = b.length - a.length;

      if (diff !== 0) diff = this._contractLookup[b].length - this._contractLookup[a].length;

      return diff;
    });
    this._contractRegexp = new RegExp(keys.join('|'), 'gi');

    // Expose class for custom word lists
    this.Contractions = Contractions;
  }

  expand(text) {
    return this._convert(text, this._expandLookup, this._expandRegexp);
  }

  contract(text) {
    return this._convert(text, this._contractLookup, this._contractRegexp);
  }

  _convert(text, lookup, regexp) {
    return text.replace(regexp, (matched) => {
      var replacement = lookup[matched.toLowerCase()];
      var firstCharCode = matched.charAt(0) === '\'' ? matched.charCodeAt(1) : matched.charCodeAt(0);

      // Check if first character of matched string is uppercase
      if (firstCharCode >= 65 && firstCharCode <= 90) {
        // Uppercase the first character of the replacement text
        if (replacement.charAt(0) === '\'') {
          replacement = '\'' + replacement.charAt(1).toUpperCase() + replacement.slice(2);
        } else {
          replacement = replacement.charAt(0).toUpperCase() + replacement.slice(1);
        }
      }

      return replacement;
    });
  }
}

module.exports = new Contractions(wordLookup);