Cache using all available memory in large document with unique strings

[lekoder]

Bug Report

Description of the problem

When generating large document (40k+ pages) with custom font and lots of unique strings, the embeded font layout cache takes up all available memory due to being populated by unique "words". This eventually causes application crash due to out of heap memory error.

Your environment

• pdfkit version: 0.8.3
• Node version: v10.6.0

Use case

Bank statements, accounting reports and other similar documents tend to have lot of unique strings (identifiers, balances, URLs, etc) and are simultaneously very large.

Workaround

An usable workaround was found: passing { features:[] } to .text() disables the cache and allows generation of document.

[liborm85]

Would be great to add option to disable cache for rendering large documents.

[blikblum]

Would be great to add option to disable cache for rendering large documents.

I will do it.

Another option is to use Map since it can get more keys: https://code.i-harness.com/en/q/1f5cefa

It would be helpful to provide an example so we can test the performance with plain object and Map

[blikblum]

Added. I'd like the opinion about the name. Technically is a fontLayoutCache but the layout is a implementation detail that regular users should not be aware