code: function getRequireExpressionModuleId(node, t) {
      if (t.isCallExpression(node)) {
          let {arguments: args, callee} = node;
          if (t.isIdentifier(callee)
              && callee.name === 'require'
              && args.length === 1
              && t.isLiteral(args[0])
          ) {
              let id = args[0].value;
              return id;
          }
      }
  }
docs: Get require expression module id
  
  @inner
  @param {Object} node the require call expression node
  @param {Object} t the bable type definition
  @return {?string}