renovate/lib/manager/npm/update.js

const _ = require('lodash');

module.exports = {
  setNewValue,
};

function setNewValue(currentFileContent, depType, depName, newVersion, logger) {
  logger.debug(`setNewValue: ${depType}.${depName} = ${newVersion}`);
  try {
    const parsedContents = JSON.parse(currentFileContent);
    // Save the old version
    const oldVersion = parsedContents[depType][depName];
    if (oldVersion === newVersion) {
      logger.debug('Version is already updated');
      return currentFileContent;
    }
    // Update the file = this is what we want
    parsedContents[depType][depName] = newVersion;
    // Look for the old version number
    const searchString = `"${oldVersion}"`;
    const newString = `"${newVersion}"`;
    let newFileContent = null;
    // Skip ahead to depType section
    let searchIndex =
      currentFileContent.indexOf(`"${depType}"`) + depType.length;
    logger.debug(`Starting search at index ${searchIndex}`);
    // Iterate through the rest of the file
    for (; searchIndex < currentFileContent.length; searchIndex += 1) {
      // First check if we have a hit for the old version
      if (matchAt(currentFileContent, searchIndex, searchString)) {
        logger.debug(`Found match at index ${searchIndex}`);
        // Now test if the result matches
        const testContent = replaceAt(
          currentFileContent,
          searchIndex,
          searchString,
          newString,
          logger
        );
        // Compare the parsed JSON structure of old and new
        if (_.isEqual(parsedContents, JSON.parse(testContent))) {
          newFileContent = testContent;
          break;
        }
      }
    }
    // istanbul ignore if
    if (!newFileContent) {
      logger.warn(
        { currentFileContent, parsedContents, depType, depName, newVersion },
        'setNewValue error'
      );
      return currentFileContent;
    }
    return newFileContent;
  } catch (err) {
    logger.info({ err }, 'setNewValue error');
    return null;
  }
}

// Return true if the match string is found at index in content
function matchAt(content, index, match) {
  return content.substring(index, index + match.length) === match;
}

// Replace oldString with newString at location index of content
function replaceAt(content, index, oldString, newString, logger) {
  logger.debug(`Replacing ${oldString} with ${newString} at index ${index}`);
  return (
    content.substr(0, index) +
    newString +
    content.substr(index + oldString.length)
  );
}