Nineteen-year-old Tibor Cifra, of Gordon Street, Leigh, admitted spitting in the face of 57-year-old Linda Evans at Leigh Library last December.
Wigan Magistrates Court heard how Cifra, who is originally from Slovakia, was less than two months into an existing community order at the time of the assault.
At about 5.30pm on December 5, a number of youths had gathered around the computers at Leigh Library.
Initially, the youths didn't cause any trouble, but when Cifra arrived a short time later the court was told that the noise level suddenly ratcheted up.
The library assistant approached the gang, asked the defendant to quieten down and returned to her desk.
When Cifra ignored her plea a second time, a supervisor asked the defendant to move away from the computers.
But as Cifra did so, he uttered a phrase in a foreign language and spat in the assistant's face.
Members of the public attempted to grab Cifra but he escaped out of the front door.
Mrs Evans subsequently told police how she was initially in shock at what had happened and simply returned to her desk.
Only when a colleague accompanied her into a back room did she eventually wash the spit off her face.
In a police statement, the victim told how she was disgusted at what Cifra did and commented on how he had no right to spit at her.
In mitigation, Cifra's defence solicitor argued that the defendant had pleaded guilty at the earliest opportunity and had shown remorse.
But Cifra was ordered to undertake 130 hours of unpaid work as part of a 12-month community order and pay £200 compensation to the victim and £35 costs.
Upon hearing the verdict, Pete Gascoigne, executive director of libraries, heritage and arts for Wigan Leisure and Culture Trust, commented: "We take a zero tolerance approach to anyone being aggressive or abusive towards our staff and will inform the police."