How to catch exception in node.js?

I have a simple script and read-only database redis.

var redis = require('redis'),
client = redis.createClient(), multi

client.on('error', function(error) {
    console.log('error')
})

tasks = []
tasks.push(['set', 'a', 1 ])
tasks.push(['set', 'b', 1 ])

client.multi(this.tasks).exec(function (err, replies) {
   console.log(err)
   tasks = []
   tasks.push(['set', 'a', 1 ])
   client.multi(tasks).exec(function (err, replies) {
   console.log(err)
   })
})

Result of this script:

null
null

/usr/local/lstat/lstat/node_modules/redis/index.js:468
                throw callback_err;
                  ^
Error: Error: Error: READONLY You can't write against a read only slave.

How to catch this exception ?