traceur/src/codegeneration/UnicodeEscapeSequenceTransformer.js

ES6 to ES5 compiler

// Copyright 2014 Traceur Authors.
//
// Licensed under the Apache License, Version 2.0 (the 'License');
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an 'AS IS' BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import {ParseTreeTransformer} from './ParseTreeTransformer.js';
import {LiteralExpression} from '../syntax/trees/ParseTrees.js';
import {LiteralToken} from '../syntax/LiteralToken.js';
import {STRING} from '../syntax/TokenType.js';

let re = /(\\*)\\u{([0-9a-fA-F]+)}/g;

function zeroPad(value) {
  return '0000'.slice(value.length) + value;
}

function needsTransform(token) {
  return token.type === STRING && re.test(token.value);
}

function transformToken(token) {
  return token.value.replace(re, (match, backslashes, hexDigits) => {
    let backslashIsEscaped = backslashes.length % 2 === 1;
    if (backslashIsEscaped) {
      return match;
    }

    let codePoint = parseInt(hexDigits, 16);
    let value;
    if (codePoint <= 0xFFFF) {
      value = '\\u' + zeroPad(codePoint.toString(16).toUpperCase());
    } else {
      let high = Math.floor((codePoint - 0x10000) / 0x400) + 0xD800;
      let low = (codePoint - 0x10000) % 0x400 + 0xDC00;
      value = '\\u' + high.toString(16).toUpperCase() +
              '\\u' + low.toString(16).toUpperCase();
    }

    return backslashes + value;
  });
}

export class UnicodeEscapeSequenceTransformer extends ParseTreeTransformer {
  transformLiteralExpression(tree) {
    let token = tree.literalToken;
    if (needsTransform(token)) {
      let value = transformToken(token);
      return new LiteralExpression(tree.location,
          new LiteralToken(STRING, value, token.location));
    }
    return tree;
  }
}